Www Mikroe Com Chapters View 69 Chapter 6 Examples

7/29/2019 Www Mikroe Com Chapters View 69 Chapter 6 Examples

1/67

pdfcrowd comopen in browser PRO version Are you a developer? Try out the HTML to PDF API

TOC Chapter 1 Chapter 2 Chapter 3 Chapter 4 Chapter 5 Chapter 6 Chapter 7

Architecture and programming of 8051 MCU's

Chapter 6 : Examples

6.1 Basic connecting of the microcontroller

6.2 Additional components

6.3 Examples

Introduction

The purpose of this chapter is to provide basic information about microcontrollers that one needs to know in order to be able to use them

success fully in practice. This is why this chapter does n't contain any super interesting program or device schematic with amazing

solutions. Ins tead, the following examples are better proof that program writing is neither a privilege nor a talent issue, but the ability of

simply putting puzzle pieces together using directives. Rest as sured that design and development of devices mainly consists of the

following method test-correct-repeat. Of course, the more you are in it, the more complicated it becomes since the puzzle pieces are put

together by both children and first-class architects...

6.1 Basic connecting

Featured Development Tools

Easy8051 v6 Development

System

The Easy8051 v6 is compatible w ith 14-,

16-, 20-, 28-, 40-pin PLCC44 and PLCC32

MCUs. It comes w ith an AT89S8253. The

board has a USB 2.0 programmer and

many peripherals such as COG, port

expander, MENU and 4x4 keypads etc.

[more info]

mikroProg for 8051

Login | Cart (0)

Products Solutions Store Distributors Libstock Contact Us Enter keywords
http://www.mikroe.com/easy8051/http://www.mikroe.com/easy8051/http://www.mikroe.com/easy8051/http://www.mikroe.com/easy8051/http://www.mikroe.com/easy8051/http://www.mikroe.com/products/view/267/architecture-and-programming-of-8051-mcu-s/http://www.mikroe.com/chapters/view/64/chapter-1-introduction-to-microcontrollers/http://www.mikroe.com/chapters/view/65/chapter-2-8051-microcontroller-architecture/http://www.mikroe.com/easy8051/http://www.mikroe.com/easy8051/http://www.mikroe.com/easy8051/http://www.mikroe.com/easy8051/http://www.mikroe.com/easy8051/http://www.mikroe.com/easy8051/http://www.mikroe.com/easy8051/http://www.mikroe.com/easy8051/http://pdfcrowd.com/http://pdfcrowd.com/redirect/?url=http%3a%2f%2fwww.mikroe.com%2fchapters%2fview%2f69%2fchapter-6-examples%2f&id=ma-130201200047-f3d925f4http://pdfcrowd.com/customize/http://pdfcrowd.com/html-to-pdf-api/?ref=pdfhttp://www.mikroe.com/products/view/267/architecture-and-programming-of-8051-mcu-s/http://www.mikroe.com/chapters/view/64/chapter-1-introduction-to-microcontrollers/http://www.mikroe.com/chapters/view/65/chapter-2-8051-microcontroller-architecture/http://www.mikroe.com/chapters/view/66/chapter-3-the-8051-instruction-set/http://www.mikroe.com/chapters/view/67/chapter-4-at89s8253-microcontroller/http://www.mikroe.com/chapters/view/68/chapter-5-assembly-language/http://www.mikroe.com/chapters/view/69/chapter-6-examples/http://www.mikroe.com/chapters/view/70/chapter-7-development-systems/http://www.mikroe.com/easy8051/http://www.mikroe.com/easy8051/http://www.mikroe.com/easy8051/http://www.mikroe.com/mikroprog/8051/http://www.mikroe.com/users/login/http://www.mikroe.com/carts/mini/http://www.mikroe.com/http://www.mikroe.com/store/http://www.mikroe.com/distributors/http://www.libstock.com/http://www.mikroe.com/visitor_contacts/


2/67


As seen in the figure above, in order to enable the m icrocontroller to operate properly it is necessary to provide:

Power supply:

Reset signal: and

Clock signal.

Clearly, it is about very simple circuits, but it does not have to be always like that. If the target device is used for controlling expensive

machines or maintaining vital functions, everything gets increas ingly complicated. However, this s olution is sufficient for the time being...

Power supply

Even though this microcontroller can operate at different power supply voltages, why to test Murphys low?! A 5V DC is mos t commonly

used. The circuit, shown in the figure, uses a cheap integrated three-terminal positive regulator LM7805, and provides high-quality voltage

stability and quite enough current to enable the microcontroller and peripheral electronics to operate normally (enough current in this case

means 1Amp).

Featured Compilers

mikroProg for 8051 is supported w ith

mikroC, mikroBasic and

mikroPascal compilers for 8051. You

may also use mikroProg for 8051 as a

standalone programming tool. [more info]

mikroBasic PRO for 8051

The 8051 core combined with modern

modules is popular in the past. With

mikroBasic you can quickly develop

your projects. [more info]
http://pdfcrowd.com/http://pdfcrowd.com/redirect/?url=http%3a%2f%2fwww.mikroe.com%2fchapters%2fview%2f69%2fchapter-6-examples%2f&id=ma-130201200047-f3d925f4http://pdfcrowd.com/customize/http://pdfcrowd.com/html-to-pdf-api/?ref=pdfhttp://www.mikroe.com/mikroprog/8051/http://www.mikroe.com/mikroprog/8051/http://www.mikroe.com/mikrobasic/8051/http://www.mikroe.com/mikrobasic/8051/http://www.mikroe.com/mikrobasic/8051/


3/67


Reset signal

In order that the mucrocontroller can operate properly, a logic 0 (0V) mus t be applied to the res et pin RS. The push button connecting the

reset pin RS to power supply VCC is not necessary. However, it is alm ost always provided because it enables the microcontroller safe

return to normal operating conditions if something goes wrong. 5V is brought to this pin, the microcontroller is reset and program starts

execution from the beginning.

Clock signal

Even though the microcontroller has a built-in oscillator, it cannot operate without two external capacitors and quartz crystal which stabilize

its operation and de termines its frequency (operating speed of the m icrocontroller).

Of course, it is not always possible to apply this s olution so that there are always

alternative ones . One of them is to provide clock signal from a special source

through invertor. See the figure on the left.

6.2 Additional components

Regardless of the fact that the microcontroller is a product of modern technology, it is of no us e without being connected to additional

components. Simply put, the appearance of voltage on its pins means nothing if not used for performing certain operations (turn

som ething on/off, shift, display etc.).

Switches and Push buttons

There are no simpler devices than switches and push-buttons. This is the simplest way of detecting appearance of a voltage on the

microcontroller input pin.

Nevertheless, it is not so simple in practice... It is about contact

bounce- a common problem with m e c h a n i c a l switches.

When the contacts s trike together, their momentum and elasticity
http://pdfcrowd.com/http://pdfcrowd.com/redirect/?url=http%3a%2f%2fwww.mikroe.com%2fchapters%2fview%2f69%2fchapter-6-examples%2f&id=ma-130201200047-f3d925f4http://pdfcrowd.com/customize/http://pdfcrowd.com/html-to-pdf-api/?ref=pdf


4/67


act together to cause bounce. The result is a rapidly pulsed

electrical current instead of a clean transition from zero to full

current. It mos tly occurs due to vibrations, slight rough s pots and

dirt between contacts. This effect is us ually unnoticeable when

using these components in everyday life because the bounce

happens too quickly. In other words, the whole this process does

not last long (a few micro- or m iliseconds), but it is long enough to

be registered by the microcontroller. When us ing only a push-

button as a pulse counter, errors occur in almost 100% of cases!

The simples t solution to this problem is to connect a simple RC circuit to suppress

quick voltage changes. Since the bounce period is not defined, the values of

components are not precisely determined. In mos t cases, it is recomended to use

the values s hown in figure below.

If complete stability is needed then radical m easures should be taken. The output of the circuit, shown in figure (RS flip-flop), will change

its logic state only after detecting the first pu lse triggered by contact bounce. This solution is expensive (SPDT switch), but effecient, the

problem is definitely solved. Since the capacitor is not used, very short pulses can also be registered in this way.

In addition to these hardware solutions , there is also a sim ple software solution.

When a program tests the state of an input pin and detects a change, the check

should be done one more time after a certain delay. If the change is confirmed, it

means that a switch or push button has changed its position. The advantages of

such s olution are obvious: it is free of charge, effects of noises are eliminated and it

can be applied to the poorer quality contacts as well. Disadvantage is the same as

when using RC filter, i.e. pulses s horter than program delay cannot be registered.

Optocoupler

An optocoupler is a device comm only used to ga lvanically

separate m icrocontrollers electronics from any potentially

dangerous current or voltage in its s urroundings. Optocouplers

usually have one, two or four light sources (LED diodes ) on their

input while on their output, opposite to diodes, there is the sam e

number of elem ents sens itive to light (phototransis tors, photo-

thyristors or photo-triacs). The point is that an optocoupler uses a


5/67


short optical transmiss ion path to transfer a signal between the

elements of circuit, while keeping them electrically isolated. This

isolation makes sens e only if diodes and photo-sens itive

elements are separately powered. In this way, the m icrocontroller

and expensive additional electronics are comp letely protected

from high voltage and noises which are the most common cause

of destroying, damaging or uns table operation of electronic

devices in practice. The most frequently used optocouplers are those with phototransistors on their outputs. When using the optocoupler

with internal base-to-pin 6 connection (there are also optocouplers without it), the base can be left unconnected. An optional connection

which lessens the effects of noises by eliminating very short pulses is pres ented by the broken line in the figure.

Relay

A relays is an electrica l switch that opens and closes under control of another electrical

circuit. It is therefore connected to ouput pins of the m icrocontroller and us ed to turn on/off

high-power devices such as motors, transformers, heaters, bulbs, antenna systems etc.

These are almost always placed away from the board sensitive components. There are

various types of relays but all of them operate in the s ame way. When a current flows through

the coil, the relay is operated by an electromagnet to open or close one or m any sets of

contacts. Sim ilar to optocouplers, there is no galvanic connection (electrical contact) between

input and output circuits. Relays us ually demand both higher voltage and current to start

operation, but there are also m iniature ones which can be activated by a low current directly

obtained from a m icrocontroller pin.

The figure shows the solution s pecific to the 8051 microcontroller. A darlington transistor is

used here to activate relays becaus e of its high current gain. This is not in accordance with

rules, but is necessary in the event that logic one activation is applied since the output

current is then very low (pin acts as an input).


6/67


In order to prevent the appearance of self-induction high voltage, caused by a s udden s top of current flow through the coil, an inverted

polarized diode is connected in parallel to the coil. The purpose of this diode is to cut off the voltage peak.

Light-emitting diode (LED)

Light-emitting diodes are elements for light signalization in electronics. They are manufactured in different shapes, colors and sizes. For

their low price, low power consumption and s imple us e, they have almos t completely pushed aside other light sources , bulbs at first place.

They perform sim ilar to common diodes with the difference that they emit light when current flows through them.

It is im portant to limit their current, otherwise they will be perm anently destroyed. For


7/67


this reason, a conductor mus t be connected in parallel to an LED. In order to

determine value of this conductor, it is necess ary to know diodes voltage drop in

forward direction, which depends on what material a diode is made from and what

colour it is. Typical values of the mos t frequently used diodes are shown in table

below. As s een, there are three main types of LEDs. Standardones get ful

brightness at current of 20mA.Low Currentdiodes get ful brightness at ten times

lower current while Super Brightdiodes produce more intens ive light than Standard

ones.

C OL OR T YPE T YPI C A L C URRENT I D ( MA ) M AX I M AL C URRENT I F ( M A ) V OL T AGE DROP UD ( V)

Infrared - 30 50 1.4

Red Standard 20 30 1.7

Red Super Bright 20 30 1.85

Red Low Current 2 30 1.7

Orange - 10 30 2.0

Green Low Current 2 20 2.1

Yellow - 20 30 2.1

Blue - 20 30 4.5

White - 25 35 4.4

Since the 8051 microcontroller can provide only low output current and since its pins

are configured as outputs when voltage provided on them is 0V, direct connecting to

LEDs is performed as shown in figure on the right (Low currentLED, cathode is

connected to the output pin).


8/67


Most commonly used is a so called 7-segment display. It is composed of 8 LEDs, 7

segm ents are arranged as a rectangle for symbol dis playing and there is an additional

segm ent for decimal point dis playing. In order to sim plify connecting, anodes and catodes

of all diodes are connected to the common pin so that there are comm on anode displays

and comm on catode displays, respectively. Segments are marked with the latters from A

to G, plus dp, as shown in the figure on the left. On connecting, each diode is treated

separtely, which means that each must have its own current limiting resistor.

LED displays

Basically, an LED display is nothing more than several LEDs moulded in the same plastic case. There are many types of displays

composed of several dozens of built in diodes which can display different symbols.

Displays connected to the microcontroller usually occupy a large num ber of valuable I/O pins, which can be a big problem especially if it is

needed to display multy digit numbers. The problem is more than obvious if, for example, it is needed to display two 6-digit numbers (a

sim ple calculation shows that 96 output pins are needed in this case). The solution to this problem is called MULTIPLEXING. This is how

an optical illusion bas ed on the sam e operating principle as a film camera is made. Only one digit is active at a time, but they change their

state so quickly making impres sion that all digits of a num ber are sim ultaneously active.


9/67

df d mi b PRO i Are you a developer? Try out the HTML to PDF API

Here is an explanation on the figure above. First a byte representing units is app lied on a microcontroller port and a transis tor T1 isactivated at the sam e time. After a while, the transis tor T1 is turned off, a byte representing tens is applied on a port and a transis tor T2 is

activated. This process is being cyclically repeated at high speed for all digits and corresponding trans istors.

The fact that the microcontroller is jus t a kind of miniature computer designed to understand only the language of zeros and ones is fully

express ed when dis playing any digit. Namely, the microcontroller doesn't know what units, tens or hundreds are, nor what ten digits we are

used to look like. Therefore, each number to be displayed mus t be prepared in the following way:

First of all, a multy digit number must be s plit into units, tens etc. in a particular subroutine. Then each of these digits mus t be stored in

special bytes. Digits get familiar format by performing m asking. In other words, a binary format of each digit is replaced by a different


10/67

df di b PRO i Are you a developer? Try out the HTML to PDF API

combination of bits in a s imple s ubroutine. For example, the digit 8 (0000 1000) is replaced by the binary number 0111 111 in order to

activate all LEDs dis playing digit 8. The only diode remaining inactive in this case is reserved for the decimal point. If a microcontroller port

is connected to the dis play in such a way that bit 0 activates segment a, bit 1 activates s egment b, bit 2 s egment c etc., then the table

below shows the mask for each digit.

DI G I T S T O DI SP L A Y DI S P L A Y SEGM ENT S


11/67

df di b PRO i A d l ? T t th HTML t PDF API

dp a b c d e f g

0 1 0 0 0 0 0 0 1

1 1 0 0 1 1 1 1 1

2 1 0 0 1 0 0 1 0

3 1 0 0 0 0 1 1 0

4 1 1 0 0 1 1 0 0

5 1 0 1 0 0 1 0 0

6 1 0 1 0 0 0 0 0

7 1 0 0 0 1 1 1 1

8 1 0 0 0 0 0 0 0

9 1 0 0 0 0 1 0 0

In addition to digits from 0 to 9, some letters of alphabet - A, C, E, J, F, U, H, L, b, c, d, o, r, t - can also be displayed by performing

appropriate masking.

If the event that comm on chatode displays are us ed all units in the table should be replaced by zeros and vice versa. Additionally, NPN

transistors should be used as drivers as well.

Liquid Crystal Displays (LCD)

An LCD display is speci fically manufactured to be used with microcontrollers, which means that it cannot be activated by standard IC

circuits. It is us ed for displaying different mess ages on a miniature liquid crysal display.

The model described here is for its low price and great

capabilities mos t frequently used in p ractice. It is based on the

HD44780 microcontroller (Hitachi) and can display messages in

two lines with 16 characters each. It displays all the letters of

alphabet, Greek letters, punctuation marks , mathematical

symbols etc. In addition, it is poss ible to display symbols made

up by the user. Other useful features include automatic message

shift (left and right), cursor appearance, LED backlight etc.

LCD Pins

There are pins along one s ide of a sm all printed board. These are used for connecting to the microcontroller. There are in total of 14 pins

marked with numbers (16 if it has backlight). Their function is described in the table bellow:


12/67df di b PRO i A d l ? T t th HTML t PDF API

FUNC T I ON P I N NUM BER NA M E L OGI C S T A T E DESC RI PT I ON

Ground 1 Vss - 0V

Power supply 2 Vdd - +5V

Contrast 3 Vee - 0 - Vdd

Control of operating

4 RS0

1

D0 D7 are interpreted as commands

D0 D7 are interpreted as data

5 R/W 01

Write data (from controller to LCD)Read data (from LCD to controller)

6 E

0

1

From 1 to 0

Access to LCD disabled

Normal operating

Data/commands are transferred to LCD

Data / commands

7 D0 0/1 Bit 0 LSB

8 D1 0/1 Bit 1

9 D2 0/1 Bit 2

10 D3 0/1 Bit 3

11 D4 0/1 Bit 4

12 D5 0/1 Bit 5

13 D6 0/1 Bit 6

14 D7 0/1 Bit 7 MSB

LCD screen

An LCD screen consis ts of two lines each contain ing 16

characters. Each character consists of 5x8 or 5x11 dot matrix. This

book covers the mos t commonly used display, i.e. the 5x8character display.

Display contrast depends on the power supply voltage and

whether mess ages are displayed in one or two lines. For this

reason, varying voltage 0-Vdd is applied on the pin m arked as

Vee. Trimmer potentiometer is us ually used for that purpose.

Some LCD displays have built-in backlight (blue or green LEDs).

When used during operation, a current limiting resis tor should be

serially connected to one of the pins for backlight power supply

( i il t LED )


13/67df di b PRO i

Are you a developer? Try out the HTML to PDF API

(similar to LEDs).

If there are no characters displayed or if all of them are dimmed when the dis play is on, the first thing that should be done is to check the

potentiometer for contrast regulation. Is it properly adjusted? The sam e applies if the mode of operation has been changed (writing in one

or two lines).

LCD Memory

The LCD display contains three memory blocks:

DDRAM Display Data RAM;

CGRAM Character Generator RAM; and

CGROM Character Generator ROM.

DDRAM Memory

DDRAM memory is us ed for storing characters to be displayed. The size of this m emory is s ufficient for storing 80 characters. Some

l ti di tl t d t th h t di l


14/67df di b PRO iAre you a developer? Try out the HTML to PDF API

mem ory locations are directly connected to the characters on display.

It works quite simply: it is sufficient to configure the display so as to increment addresses automa tically (shift right) and set the starting

address for the mess age that should be dis played (for example 00 hex).

After that, all characters sent through lines D0-D7 will be dis played in the mess age format we are used to- from le ft to right. In this case,

displaying starts from the first field of the first line since the address is 00 hex. If more than 16 characters are s ent, then all of them will be

mem orized, but only the first s ixteen characters will be visible. In order to display the rest of them, a shift comm and should be us ed.

Virtually, everything looks as if the LCD dis play is a window which moves left-right over mem ory locations containing different characters.

This is how the effect of mess age moving on the screen is made.

If the cursor is on, it appears at the location which is currently addressed. In other words, when a character appears at the cursor position,

it will automatically move to the next addressed location.

Since this is a sort of RAM memory, data can be written to and read from it, but its contents is irretrievably lost when the power goes off.

CGROM Memory

CGROM memory contains the default chracter map with all characters that can be dis played on the screen. Each character is ass igned to

one mem ory location.


15/67df di b PRO iAre you a developer? Try out the HTML to PDF API


16/67

Are you a developer? Try out the HTML to PDF API

The address es of CGROM memory locations m atch the characters of ASCII. If the program being currently executed encounters a

command send character P to port, then the binary value 0101 0000 appears on the port. This value is the ASCII equivalent to the

character P. It is then written to LCD, which results in displaying the symbol from 0101 0000 location of CGROM. In other words, the

character P is dis played. This applies to all letters of alphabet (capitals and s mall), but not to numbers.

As seen on the previous m ap, addres ses of all digits are pus hed forward by 48 relative to their values (dig it 0 address is 48, digit 1

address is 49 , digit 2 address is 50 etc.). Accordingly, in order to display digits correctly, each of them needs to be added a decimal

number 48 prior to be sent to LCD.

From their inception till today, computers can recognize only numbers, but not letters. It means that all data a computer s waps with a

peripheral device has a binary format, even though the same is recognized by the man as letters (keyboard is an excellent example). Every

character matches the unique com bination of zeroes and ones. ASCII is character encoding based on the English alphabet. ASCII code

specifies correspondance between standard character symbols and their numerical equivalents.

CGRAM memory

Apart from standard characters , the LCD disp lay can also dis play symbols defined by the user itsel f. It can be any symbol in the size of 5x8

pixels. RAM memory called CGRAM in the size of 64 bytes enables it.

Memory registers are 8 bits wide, but only 5 lower bits are us ed. Logic one (1) in every register represents a dimm ed dot, while 8 locations

grouped together represent one character. It is best illus trated in figure below:


17/67

pdfcrowd.comopen in browser PRO version Are you a developer? Try out the HTML to PDF API

Symbols are usually defined at the beginnig of the program by simply writing zeros and ones to regis ters of CGRAM memory so that they

form des ired shapes . In order to display them it is sufficient to specify their address. Pay attention to the first coloumn in the CGROM map

of characters. It doesn't contain RAM memory addresses , but symbols being dis cussed here. In this example, display 0 means - display

, display 1 means - display etc.

LCD Basic Commands

All data transferred to LCD through the outputs D0-D7 wil l be interpreted as a com mand or a data, which depends on the pin RS log ic

state:

RS = 1 - Bits D0-D7 are address es of the characters to be displayed. LCD processor addresses one character from the character map and

displays it. The DDRAM address s pecifies the location on which the character is to be displayed. This address is defined before the


18/67


p y p p y

character is transferred or the address of previously transferred character is au tomatically incremented.

RS = 0 - Bits D0 - D7 are comm ands which determine the display mode. The commands recognized by the LCD are given in the table

below:

C OM M A ND RS RW D7 D6 D5 D4 D3 D2 D1 D0 EX EC UT I ON T I M E

Clear display 0 0 0 0 0 0 0 0 0 1 1.64mS

Cursor home 0 0 0 0 0 0 0 0 1 x 1.64mS

Entry mode set 0 0 0 0 0 0 0 1 I/D S 40uS

Display on/off control 0 0 0 0 0 0 1 D U B 40uS

Cursor/Display Shift 0 0 0 0 0 1 D/C R/L x x 40uS

Function set 0 0 0 0 1 DL N F x x 40uS

Set CGRAM address 0 0 0 1 CGRAM address 40uS

Set DDRAM address 0 0 1 DDRAM address 40uS

Read BUSY flag (BF) 0 1 BF DDRAM address -

Write to CGRAM or DDRAM 1 0 D7 D6 D5 D4 D3 D2 D1 D0 40uS

Read from CGRAM or DDRAM 1 1 D7 D6 D5 D4 D3 D2 D1 D0 40uS

I/D 1 = Increment (by 1) R/L 1 = Shift right

0 = Decrement (by 1) 0 = Shift left

S 1 = Display shift on DL 1 = 8-bit interface

0 = Display shift off 0 = 4-bit interface

D 1 = Display on N 1 = Display in two lines

0 = Display off 0 = Display in one line

U 1 = Cursor on F 1 = Character format 5x10 dots

0 = Cursor off 0 = Character format 5x7 dots

B 1 = Cursor blink on D/C 1 = Display shift

0 = Cursor blink off 0 = Cursor shift


19/67


What is the Busy flag?

Compared to the m icrocontroller, the LCD is an extremely slow com ponent. Because of this, it was necessary to provide a signal which

will, upon command execution, indicate that the display is ready to receive a new data. That s ignal, called the bus y flag, can be read from

line D7. When the BF bit is cleared (BF=0), the display is ready to receive a new data.

LCD Connection

Depending on how m any lines are used for connecting the LCD to the microcontroller, there are 8-bit and 4-bit LCD modes. Theappropriate mode is selected at the beginning of the operation. This process is called initialization. 8-bit LCD mode uses outputs D0-D7

to transfer data in the way explained on the previous page. The m ain purpose of 4-bit LED mode is to save valuable I/O pins of the

microcontroller. Only 4 higher bits (D4-D7) are us ed for comm unication, while other may be left unconnected. Each data is s ent to the LCD

in two steps : four higher bits are s ent first (normally through the lines D4-D7), then four lower bits. Initialization enables the LCD to link and

interpret received bits correctly. Data is rarely read from the LCD (it is mainly transferred from the m icrocontroller to LCD) s o that it is often

poss ible to save an extra I/O pin by simple connecting R/W pin to ground. Such saving has its price. Messages will be normally displayed,

but it will not be possible to read the busy flag since it is not poss ible to read the display either.


20/67


Fortunately, there is a s imple s olution. After sending a character or a command it is important to give the LCD enough time to do its job.

Owing to the fact that execution of the s lowest command lasts for approximately 1.64mS, it will be sufficient to wait approximately 2mS for

LCD.

LCD Initialization

The LCD is automatically cleared when powered up. It las ts for approximately 15mS. After that, the display is ready for operation. The mode

of operation is s et by default. It means that:


21/67


Automatic reset is in m ost cases performed without any problem s. In most cas es, but not always! If for any reason the power supply

voltage does not reach ful value within 10mS, the dis play will start to perform com pletely unpredictably. If the voltage supply unit is not able

to meet this condition or if it is needed to provide completely safe operation, the process of initialization is applied. Initialization, among

other things, causes a new reset enabling dis play to operate normally.

Refer to the figure below for the procedure on 8-bit initialization:

1. Display is cleared

2. Mode

3. Display/Cursor on/off

4. Character entry

DL = 1 Communication through 8-bit interface

N = 0 Messages are displayed in one line

F = 0 Character f ont 5 x 8 dots

D = 0 Display off

U = 0 Cursor off

B = 0 Cursor blink off

ID = 1 Displayed addresses are automatically incremented by 1

S = 0 Display shift of f


22/67


It is not a mistake!

I thi l ith th l i t f d th ti i


23/67


In this algorithm, the sam e value is transferred three times in a row.

In case of 4-bit initialization, the procedure is as follows:


24/67


6.3 Examples

The schematic below is used in the several following examples:


25/67


Apart from components neces sary for the operation o f the microcontroller such as osci llator with capaci tors and the sim ples t reset circuit,

there are also s everal LEDs and one push button. These are used to indicate the operation of the program.

All LEDs are polarized in such a way that they are activated by driving a m icrocontroller pin low (logic 0).

LED Blinking

The purpose of this example is not to dem onstrate the operation of LEDs, but the operating speed of the microcontroller. Simply put, in


26/67


order to enable LED blinking to be visible, it is necessa ry to provide sufficient amount of time to pass be tween on/off states of LEDs. In this

example time delay is provided by executing a subroutine called Delay. It is a triple loop in which the program remains for approximately

0.5 seconds and decrements values s tored in registers R0, R1 or R2. After returning from the subroutine, the pin state is inverted and the

sam e procedure is repeated...

;************************************************************************

;* PROGRAM NAME : Delay.ASM

;* DESCRIPTION: Program turns on/off LED on the pin P1.0;* Software delay is used (Delay).

;************************************************************************

;BASIC DIRECTIVES

$MOD53

$TITLE(DELAY.ASM)

$PAGEWIDTH(132)

$DEBUG

$OBJECT

$NOPAGING

;STACK

DSEG AT 03FH

STACK_START: DS 040H

;RESET VECTORS

CSEG AT 0

JMP XRESET ;Reset vector

ORG 100H

XRESET: MOV SP,#STACK_START ;Define Stack pointer

MOV P1,#0FFh ;All pins are configured as inputs

LOOP:

CPL P1.0 ;Pin P1.0 state is inverted

LCALL Delay ;Time delay

SJMP LOOP

Delay:


27/67


Delay:

MOV R2,#20 ;500 ms time delay

F02: MOV R1,#50 ;25 ms

F01: MOV R0,#230

DJNZ R0,$

DJNZ R1,F01

DJNZ R2,F02

END ;End of program

Using Watch-dog Timer

This example describes how the watch-dog timer should not operate. The watch-dog timer is properly adjusted (nominal time for counting

is 1024mS), but instruction used to res et it is intentionally left out so that this timer always "wins". As a result, the microcontroller is res et

(state in registers rem ains unchanged), program s tarts execution from the beginning and the number in register R3 is increm ented by 1

and then copied to port P1.

LEDs dis play this number in binary format...

;************************************************************************

;* PROGRAM NAME : WatchDog.ASM

;* DESCRIPTION : After watch-dog reset, program increments number in

;* register R3 and shows it on port P1 in binary format.

;************************************************************************

;BASIC DIRECTIVES

$MOD53

$TITLE(WATCHDOG.ASM)$PAGEWIDTH(132)

$DEBUG

$OBJECT

$NOPAGING

WMCON DATA 96H

WDTEN EQU 00000001B ; Watch-dog timer is enabled

PERIOD EQU 11000000B ; Nominal Watch-dog period is set to be 1024ms

;RESET VECTOR


28/67


;

CSEG AT 0

JMP XRESET ; Reset vector

CSEG

ORG 100H

XRESET: ORL WMCON,#PERIOD ; Define Watch-dog period

ORL WMCON,#WDTEN ; Watch-dog timer is enabled

MOV A,R3 ; R3 is moved to port 1

MOV P1,A

INC R3 ; Register R3 is incremented by 1

LAB: SJMP LAB ; Wait for watch-dog reset

END ; End of program

Timer T0 in mode 1

This program s pends m ost of its time in an endless loop waiting for timer T0 to count up a full cycle. When it happens, an interrupt is

generated, routine TIM0_ISRis executed and logic zero (0) on port P1 is shifted right by one bit. This is another way of demonstrating the

operating speed of the microcontroller since each shift means that counter T0 has counted up 216 pulses!

;************************************************************************

;* PROGRAM NAME : Tim0Mod1.ASM

;* DESCRIPTION: Program rotates "0" on port 1. Timer T0 in mode 1 is

;* used

;************************************************************************

;BASIC DIRECTIVES

$MOD53

$TITLE(TIM0MOD1.ASM)

$PAGEWIDTH(132)

$DEBUG

$OBJECT


29/67


$NOPAGING

;DECLARATION OF VARIABLES

;STACK

DSEG AT 03FH


;RESET VECTORS

CSEG AT 0


ORG 00BH

JMP TIM0_ISR ; Timer T0 reset vector

ORG 100H

XRESET: MOV SP,#STACK_START ; Define Stack pointer

MOV TMOD,#01H ; MOD1 is selected

MOV A,#0FFH

MOV P1,#0FFH

SETB TR0 ; Timer T0 is enabled

MOV IE,#082H ; Interrupt enabled

CLR C

LOOP1: SJMP LOOP1 ; Remain here

TIM0_ISR: RRC A ; Rotate accumulator A through Carry flag

MOV P1,A ; Contents of accumulator A is moved to PORT1

RETI ; Return from interrupt


Timer T0 in Split mode

Si il l t th i l th d t f it ti i l ll d LOOP1 Si 16 bit Ti T0 i lit i t t 8 bit


30/67


Similarly to the previous example, the program s pends m ost of its time in a loop called LOOP1. Since 16-bit Timer T0 is split into two 8-bit

timers, there are also two interrupt sources.

The first interrupt is generated after timer T0 reset. Routine TIM0_ISR in which logic zero (0) bit on port P1 rotates is executed. Outside

looking, it seems that LEDs move.

Another interrupt is generated upon Timer T1 reset. Routine TIM1_ISR in which the bit s tate DIRECTION inverts is executed. Since this bit

determines direction of bit rotation then the moving direction of LED is also changed.

If you press a push button T1 at some point, a logic zero (0) on the P3.2 output will disable Timer T1.

;************************************************************************

;* PROGRAM NAME : Split.ASM

;* DESCRIPTION: Timer TL0 rotates bit on port P1, while TL1 determines

;* the rotation direction. Both timers operate in mode

;* 3. Logic zero (0) on output P3.2 disables rotation on port P1.

;************************************************************************

;BASIC DIRECTIVES

$MOD53

$TITLE(SPLIT.ASM)

$PAGEWIDTH(132)

$DEBUG

$OBJECT

$NOPAGING


BSEG AT 0

;DECLARATION OF BIT-VARIABLES

SEMAPHORE: DBIT 8

DIRECTION BIT SEMAPHORE

;STACK

DSEG AT 03FH



31/67


;RESET VECTORS

CSEG AT 0


ORG 00BH


ORG 01BH


ORG 100H


MOV TMOD,#00001011B ; Define MOD3

MOV A,#0FFH

MOV P1,#0FFH

MOV R0,#30D

SETB TR0 ; TL0 is turned on

SETB TR1 ; TL1 is turned on

MOV IE,#08AH ; Interrupt enabled

CLR C

CLR DIRECTION ; Rotate to the right


TIM0_ISR:

DJNZ R0,LAB3 ; Slow down rotation by 256 times

JB DIRECTION,LAB1

RRC A ; Rotate contents of Accumulator to the right through

; Carry flag

SJMP LAB2

LAB1: RLC A ; Rotate contents of Accumulator to the left through

; Carry flag

LAB2: MOV P1,A ; Contents of Accumulator is moved to port P1

LAB3: RETI ; Return from interrupt


32/67


TIM1_ISR:

DJNZ R1,LAB4 ; Slow down direction of rotation by 256 times

DJNZ R2,LAB4 ; When time expires, change rotation direction

CPL SMER

MOV R2,#30D

LAB4: RETI


Simultaneous use of timers T0 and T1

This program can be considered as continuation of the previous one. They share the same idea, but in this case true timers T0 and T1 are

used. In order to demons trate the operation of both timers on the s ame port at the sam e time, timer T0 reset is used to s hift logic zero (0)

on the port, while Timer T1 reset is used to change rotation direction. This program spends mos t of its time in the loop LOOP1 waiting for

an interrupt to be caus ed by reset. By checking the DIRECTION bit, information on rotation direction of both bits in accumulator as well as

of moving port LED is obtained.

;************************************************************************

;* PROGRAM NAME : Tim0Tim1.ASM

;* DESCRIPTION: Timer TO rotates bit on port P1 while Timer1

;* changes rotation direction. Both timers are configured to operate in mode 1.

;************************************************************************

;BASIC DIRECTIVES

$MOD53$TITLE(TIM0TIM1.ASM)

$PAGEWIDTH(132)

$DEBUG

$OBJECT

$NOPAGING


BSEG AT 0


33/67


;DECLARATION OF BIT-VARIABLES

SEMAPHORE: DBIT 8

DIRECTION BIT SEMAPHORE

;STACK

DSEG AT 03FH


;RESET VECTORS

CSEG AT 0


ORG 00BH ; Timer 0 Reset vector

JMP TIM0_ISR

ORG 01BH ; Timer 1 Reset vector

JMP TIM1_ISR

ORG 100H


MOV TMOD,#11H ; Select MOD1 for both timers

MOV A,#0FFH

MOV P1,#0FFH

MOV R0,#30D ; R0 is initializedSETB TR0 ; TIMER0 is turned on

SETB TR1 ; TIMER1 is turned on

MOV IE,#08AH ; Timer0 and Timer1 Interrupt enabled

CLR C

CLR DIRECTION ; Rotate to the right


TIM0_ISR:

JB DIRECTION LAB1


34/67


JB DIRECTION,LAB1

RRC A ; Rotate contents of accumulator to the right through

; Carry flag

SJMP LAB2

LAB1: RLC A ; Rotate contents of Accumulator to the left through

; Carry flag

LAB2: MOV P1,A ; Contents of Accumulator is moved to port P1


TIM1_ISR:

DJNZ R0,LAB3 ; When time expires, change rotation direction

CPL DIRECTION

MOV R0,#30D ; Initialize R0

LAB3:

RETI


Using Timer T2

This example describes the use of Timer T2 configured to operate inAuto-Reloadmode. In this very case, LEDs are connected to port P3

while the push button used for forced timer res et (T2EX) is connected to the P1.1 pin.

Program execution is s imilar to the previous examples . When timer ends counting, an interrupt is enabled and subroutine TIM2_ISRis

executed, thus rotating a logic zero (0) in accumulator and moving the contents of accumulator to the P3 pin. At last, flags which caused an

interrupt are cleared and program returns to the loop LOOP1 where it remains until a new interrupt request arrives...

If push button T2EX is pressed, timer is temporarily reset. This push button resets timer, while push button RESET resets the

microcontroller.


35/67


;************************************************************************

;* PROGRAM NAME : Timer2.ASM

;* DESCRIPTION: Program rotates log. "0" on port P3. Timer2 determines

;* the speed of rotation and operates in auto-reload mode;************************************************************************

;BASIC DIRECTIVES

$MOD53

$TITLE(TIMER2.ASM)

$PAGEWIDTH(132)

$DEBUG

$OBJECT

$NOPAGING


36/67


;DEFINITION OF VARIABLES

T2MOD DATA 0C9H

;STACK

DSEG AT 03FH


;RESET VECTORS

CSEG AT 0


ORG 02BH ; Timer T2 Reset vector

JMP TIM2_ISR

ORG 100H


MOV A,#0FFH

MOV P3,#0FFH

MOV RCAP2L,#0FH ; Prepare 16-bit auto-reload mode

MOV RCAP2L,#01H

CLR CAP2 ; Enable 16-bit auto-reload mod

SETB EXEN2 ; Pin P1.1 reset is enabled

SETB TR2 ; Enable Timer T2

MOV IE,#0A0H ; Interrupt is enabled

CLR C


TIM2_ISR: RRC A ; Rotate contents of Accumulator to the right through

; Carry flag

MOV P3,A ; Move the contents of Accumulator A to PORT3

CLR TF2 ; Clear timer T2 flag TF2

CLR EXF2 ; Clear timer T2 flag EXF2




37/67



Using External Interrupt

Here is another example of interrupt execution. An external iterrupt is generated when a logic zero (0) is present on pin P3.2 or P3.3.

Depending on which input is active, one of two routines will be executed:

A logic zero (0) on the P3.2 pin in itiates execution of interrupt routine Is r_Int0, thus incrementing num ber in register R0 and copying it to port

P0. Logic zero on the P3.3 pin initiates execution of subroutine Isr_Int1, number in regis ter R1 is incremented by 1 and then copied to port

P1.

In short, each press on push buttons INT0 and INT1 will be counted and immediately shown in binary format on appropriate port (LED

which emitts light represents a logic zero (0)).


38/67


;************************************************************************

;* PROGRAM NAME : Int.ASM

;* DESCRIPTION : Program counts interrupts INT0 generated by appearance of high-to-low

;* transition signal on pin P3.2 Result appears on port P0. Interrupts INT1 are also

;* counted up at the same time. They are generated byappearing high-to-low transition

;* signal on pin P3. The result appears on port P1.

;************************************************************************

;BASIC DIRECTIVES

$MOD53

$TITLE(INT.ASM)


39/67


$PAGEWIDTH(132)

$DEBUG

$OBJECT

$NOPAGING

;RESET VECTORS

CSEG AT 0


ORG 003H ; Interrupt routine address for INT0

JMP Isr_Int0

ORG 013H ; Interrupt routine address for INT1

JMP Isr_Int1

ORG 100H

XRESET:MOV TCON,#00000101B ; Interrupt INT0 is generated by appearing

; high-to-low transition signal on pin P3.2

; Interrupt INT0 is generated by appearing

; high-to-low transition signal on pin P3.3

MOV IE,#10000101B ; Interrupt enabled

MOV R0,#00H ; Counter starting value

MOV R1,#00H

MOV P0,#00H ; Reset port P0

MOV P1,#00H ; Reset port P1

LOOP: SJMP LOOP ; Remain here

Isr_Int0:

INC R0 ; Increment value of interrupt INT0 counter

MOV P0,R0

RETI

Isr_Int1:

INC R1 ; Increment value of interrupt INT1 counter

MOV P1,R1


40/67


RETI


Using LED display

The following examples describe the use of LED displays. Common chatode dis plays are us ed here, which means that all built-in LEDs

are polarized in such a way that their anodes are connected to the microcontroller pins. Since the common way of thinking is that logic one(1) turns something on and logic zero (0) turns something of, Low Current displays (low power consum ption) and their diodes (segments)

are connected serially to resistors of relatively high resistance.

In order to save I/O pins, four LED displays are connected to operate in multiplex mode. It means that all segments having the sam e name

are connected to one output port each and only one display is active at a time.

Tranzistors and s egmenats on displays are quickly activated, thus making impress ion that all digits are active sim ultaneously.


41/67


Writing digits on LED display

This program is a kind of warming up exerciese before real work starts. The purpose of this example is to display something on any

display. Multiplex mode is not us ed this tim e. Instead, digit 3 is displayed on only one of them (first one on the right).

Since the microcontroller does not know how we write number 3, a sm all subroutine called Disp is us ed (the microcontroller writes this

number as 0000 0011). This subroutine enables all decimal digits (0-9) to be displayed (masked). The principle of operation is sim ple. A

number to be dis played is added to the current address and program jump is executed. Different numbers require different jump length.


42/67


p y p g j p q j p g

Precisely determined combination of zeroes and ones appears on each of these new locations (digit 1 mas k, digit 2 mask...digit 9 mask).

When this combination is transferred to the port, the display shows des ired digit.

;************************************************************************

;* PROGRAM NAME : 7Seg1.ASM

;* DESCRIPTION: Program displays number "3" on 7-segment LED display

;************************************************************************

;BASIC DIRECTIVES

$MOD53

$TITLE(7SEG1.ASM)

$PAGEWIDTH(132)

$DEBUG

$OBJECT

$NOPAGING

;STACK

DSEG AT 03FH


;RESET VECTORS

CSEG AT 0


ORG 100H


MOV P1,#0 ; Turn off all segments on displays

MOV P3,#20h ; Activate display D4

LOOP:

MOV A,#03 ; Send number 3 to display

LCALL Disp ; Perform appropriate masking for the number

MOV P1,A

SJMP LOOP


43/67


Disp: ; Subroutine for displaying digits

INC A

MOVC A,@A+PC

RET

DB 3FH ; Digit 0 mask

DB 06H ; Digit 1 maskDB 5BH ; Digit 2 mask


DB 66H ; Digit 4 mask

DB 6DH ; Digit 5 mask






Writing and changing digits on LED display

This program is only an extended verson of the previous one. There is only one digit active- the first one on the right, and there is no use of

multiplexing. Unlike the previous example, all decim al numbers are displayed (0-9). In order to enable digits to change at reas onable

pace, a soubroutine L2 which causes a short time delay is executed prior to each change occurs. Basically, the whole process is very

sim ple and takes place in the main loop called LOOP which looks as follows:

;************************************************************************

;* PROGRAM NAME: 7Seg2.ASM

1. R3 is copied to Accumulator and subroutine for masking digits Disp is executed;

2. Accumulator is copied to the port and displayed;

3. The contents of the R3 register is incremented;

4. It is checked whether 10 cycles are counted or not. If it is, register R3 is reset in order to enable counting to start

from 0; and

5. Instruction labeled as L2 within subroutine is executed.

;* DESCRIPTION: Program writes numbers 0-9 on 7-segment LED display

;************************************************************************


44/67


;BASIC DIRECTIVES

$MOD53

$TITLE(7SEG2.ASM)

$PAGEWIDTH(132)

$DEBUG

$OBJECT$NOPAGING

;STACK

DSEG AT 03FH


;RESET VECTORS

CSEG AT 0


ORG 100H


MOV R3,#0 ; Counter initial value

MOV P1,#0 ; Turn off all display segments


LOOP:

MOV A,R3

LCALL Disp ; Perform appropriate masking for number in

; Accumulator

MOV P1,A

INC R3 ; Increment number in register by 1

CJNE R3,#10,L2 ; Check whether the number 10 is in R3

MOV R3,#0 ; If it is, reset counter

L2:

MOV R2,#20 ; 500 mS time delay

F02: MOV R1,#50 ; 25 mS

F01: MOV R0,#230

DJNZ R0,$

DJNZ R1 F01


45/67


DJNZ R1,F01

DJNZ R2,F02

SJMP LOOP

Disp: ; Subroutine for writing digits

INC A

MOVC A,@A+PC

RET



DB 5BH ; Digit 2 mask






DB 7FH ; Digit 8 maskDB 6FH ; Digit 9 mask


Writing two-digit number on LED display

It is time for time m ultiplexing! This is the s imples t example which dis plays the number 23 on two displays in such a way that one of them

displays units, while the other displays tens. The most im portant thing in the program is time s ynchronization. Otherwise, everything is very

sim ple. Transistor T4 enables display D4 and at the sam e time a bit comb ination corresponding to the digit 3 is set on the port. After that,

transistor T4 is dis abled and the whole process is repeated us ing transistor T3 and display D3 in order to display digit 2. This procedure

mus t be continuosly repeated in order to make im press ion that both displays are active at the same time.

;************************************************************************

;* PROGRAM NAME: 7Seg3.ASM

;* DESCRIPTION: Program displays number "23" on 7-segment LED display

;************************************************************************

;BASIC DIRECTIVES

$MOD53

$TITLE(7SEG3 ASM)


46/67


$TITLE(7SEG3.ASM)

$PAGEWIDTH(132)

$DEBUG

$OBJECT

$NOPAGING

;STACKDSEG AT 03FH


;RESET VECTORS

CSEG AT 0


ORG 100H


LOOP: MOV P1,#0 ; Turn off all display segments


MOV A,#03 ; Write digit 3 on display D4

LCALL Disp ; Find appropriate mask for that digit

MOV P1,A ; Put the mask on the port

MOV P1,#0 ; Turn off all dislay segments



LCALL Disp ; Find mask for that digit


SJMP LOOP ; Return to the label LOOP


INC A

MOVC A,@A+PC

RET







47/67









Using four digit LED display

In this example all four displays, instead of two, are active so that it is pos sible to write numbers from 0 to 9999. Here, the number 1 234 is

displayed. After initialization, the program remains in the loop LOOP where digital multiplexing is performed. The subroutine Dis p is used

to convert binary numbers into corresponding combinations of bits for the purpose of activating display lighting segm ents.

;************************************************************************

;* PROGRAM NAME : 7Seg5.ASM

;* DESCRIPTION : Program displays number"1234" on 7-segment LED display

;************************************************************************

;BASIC DIRECTIVES

$MOD53

$TITLE(7SEG5.ASM)

$PAGEWIDTH(132)

$DEBUG$OBJECT

$NOPAGING

;STACK

DSEG AT 03FH


;RESET VECTORS

CSEG AT 0



48/67


ORG 100H


LOOP: MOV P1,#0 ; Turn off all display segments











MOV P3,#08h ; Activate display D2MOV A,#02 ; Write digit 2 on display D2








SJMP LOOP ; Return to the lable LOOP


INC A

MOVC A,@A+PC

RET









49/67






LED display as a two digit counter

Things are getting complicated... In addition to two digit multiplexing, the microcontroller also performs other operations. In this example,

contents of registers R2 and R3 are incremented in order to dis play number counting (97, 98, 99, 00, 01, 02...).

This time, transis tors which activate displays rem ain turned on for 25m S. The soubroutine Delay is in charge of that. Even though digits

shift much slower now, it is still not slow enough to make impress ion of simultaneous operation. After both digits of a number blink for 20

times, the number on displays is incremented by 1 and the whole procedure is repeated.

;************************************************************************;* PROGRAM NAME : 7Seg4.ASM

;* DESCRIPTION: Program displays numbers 0-99 on 7-segment LED displays

;************************************************************************

;BASIC DIRECTIVES

$MOD53

$TITLE(7SEG4.ASM)

$PAGEWIDTH(132)

$DEBUG

$OBJECT

$NOPAGING

;STACK

DSEG AT 03FH


;RESET VECTORS

CSEG AT 0



50/67


ORG 100H


MOV R2,#0 ; Counter starting value

MOV R3,#0

MOV R4,#0

LOOP: INC R4 ;Wait for display to be "refreshed" for 100 times

CJNE R4,#20d,LAB1 ;before incrementing the counter

MOV R4,#0


INC R2 ; Increment Register containing units by 1

CJNE R2,#10d,LAB1

MOV R2,#0 ; Reset units

INC R3 ; Increment Register with tens by 1

CJNE R3,#10d,LAB1 ;MOV R3,#0 ; Reset tens

LAB1:


MOV A,R2 ; Copy Register containing units to A

LCALL Disp ; Call mask for that digit

MOV P1,A ; Write units on display D4

LCALL Delay ; 25ms delay


MOV P3,#10h ; Activate display D3MOV A,R3 ; Copy Register contaning tens to A

LCALL Disp ; Call mask for that digit

MOV P1,A ; Write tens on display D3

LCALL Delay ; 25ms delay

SJMP LOOP

Delay:

MOV R1,#50 ; 5 ms delay

F01: MOV R0,#250

DJNZ R0,$

DJNZ R1,F01


51/67


RET

Disp: ; Subroutine for displaying digits

INC A

MOVC A,@A+PC

RET












Handling EEPROM

This program writes data to on-chip EEPROM memory. In this case, the data is a hexadecimal number 23 which is to be written to the

location with address 00.

To make s ure that this number is correctly written, the sam e location of EEPROM is read 10m S later in order to compare these two

numbers . If they match, F will be displayed. Otherwise, E will be dis played on the LED dis play (Error).

;************************************************************************

;* PROGRAM NAME: EEProm1.ASM

;* DESCRIPTION: Programming EEPROM at address 0000hex and displaying message

;* on LED display.

;************************************************************************

;BASIC DIRECTIVES

$MOD53

$TITLE(EEPROM1.ASM)


52/67


$PAGEWIDTH(132)

$DEBUG

$OBJECT

$NOPAGING

WMCON DATA 96H

EEMEN EQU 00001000B ; Access to internal EEPROM is enabled

EEMWE EQU 00010000B ; Write to EEPROM is enabled

TEMP DATA 030H ; Define Auxiliary register

THE END EQU 071H ; Display "F"

ERROR EQU 033H ; Display "E"

;STACK

DSEG AT 03FH


;RESET VECTORS

CSEG AT 0


ORG 100H

XRESET: MOV IE,#00 ; All interrupts are disabled

MOV SP,#STACK_START

MOV DPTR,#0000H ; Choose location address in EEPROM

ORL WMCON,#EEMEN ; Access to EEPROM is enabled

ORL WMCON,#EEMWE ; Write to EEPROM is enabled

MOV TEMP,#23H ; Number written to EEPROM is moved to

MOV A,TEMP ; register TEMP and Accumulator

MOVX @DPTR,A ; Write byte to EEPROM

CALL DELAY ; 10ms delay

MOVX A,@DPTR ; Read the same location and compare to TEMP,CJNE A,TEMP,ERROR ; If they don't match, jump to label ERROR

MOV A,#KRAJ ; Display F (correct)

MOV P1,A


53/67


XRL WMCON,#EEMWE ; Write to EEPROM is disabled

XRL WMCON,#EEMEN ; Access to EEPROM is disabled


ERROR: MOV A,#ERROR ; Display E (error)

MOV P1,A

LOOP2: SJMP LOOP2

DELAY: MOV A,#0AH ; Delay

MOV R3,A

LOOP3: NOP

LOOP4: DJNZ B,LOOP4

LOOP5: DJNZ B,LOOP5

DJNZ R3,LOOP3

RET


Data reception via UART

In order to enable s uccessful UART serial communication, it is necess ary to meet specific rules of the RS232 s tandard. It primarily refers

to voltage levels required by this standard. Accordingly, -10V stands for logic one (1) in the m essage, while +10V stands for logic zero (0).

The microcontroller converts accurately data into serial format, but its power supply voltage is only 5V. Since it is not easy to convert 0V into

10V and 5V into -10V, this operation is on both transmit and receive side left to a specialized IC circuit. Here, the MAX232 by MAXIM is used

because it is wides pread, cheap and reliable.

This example shows how to receive mes sage sent by a PC. Timer T1 generates boud rate. Since the 11.0592 MHz quartz crystal is used

here, it is easy to obtain standard baud rate which amouts to 9600 bauds. Each received data is im mediately transferred to port P1 pins.


54/67


;************************************************************************

;* PROGRAM NAME : UartR.ASM;* DESCRIPTION: Each data received from PC via UART appears on the port

;* P1.

;*

;************************************************************************

;BASIC DIRECTIVES

$MOD53$TITLE(UARTR.ASM)

$PAGEWIDTH(132)

$DEBUG

$OBJECT


55/67


$OBJECT

$NOPAGING

;STACK

DSEG AT 03FH


;RESET VECTORS

CSEG AT 0


ORG 023H ; Starting address of UART interrupt routine

JMP IR_SER

ORG 100H

XRESET: MOV IE,#00 ; All interrupts are disabledMOV SP,#STACK_START ; Initialization of Stack pointer

MOV TMOD,#20H ; Timer1 in mode2

MOV TH1,#0FDH ; 9600 baud rate at the frequency of

; 11.0592MHz

MOV SCON,#50H ; Receiving enabled, 8-bit UART

MOV IE,#10010000B ; UART interrupt enabled

CLR TI ; Clear transmit flag

CLR RI ; Clear receive flag

SETB TR1 ; Start Timer1


IR_SER: JNB RI,OUTPUT ; If any data is received,

; move it to the port

MOV A,SBUF ; P1

MOV P1,A


OUTPUT RETI



56/67


Data transmission via UART

This program des cribes how to use UART to transm it data. A sequence of numbers (0-255) is transmitted to a PC at 9600 baud rate. The

MAX 232 is used as a voltage regulator.

;************************************************************************;* PROGRAM NAME : UartS.ASM

;* DESCRIPTION: Sends values 0-255 to PC.

;************************************************************************

;BASIC DIRECTIVES

$MOD53

$TITLE(UARTS.ASM)

$PAGEWIDTH(132)

$DEBUG

$OBJECT

$NOPAGING

;STACK

DSEG AT 03FH


;RESET VECTORS

CSEG AT 0


ORG 100H

XRESET: MOV IE,#00 ; All interrupts are disabled

MOV SP,#STACK_START ; Initialization of Stack pointer

MOV TMOD,#20H ; Timer1 in mode 2

MOV TH1,#0FDH ; 9600 baud rate at the frequency of; 11.0592MHz

MOV SCON,#40H ; 8-bit UART

CLR TI ; Clear transmit bit



57/67



MOV R3,#00H ; Reset caunter

SETB TR1 ; Start Timer 1

START: MOV SBUF,R3 ; Move number from counter to a PC

LOOP1: JNB TI,LOOP1 ; Wait here until byte transmission is

; complete

CLR TI ; Clear transmit bit

INC R3 ; Increment the counter value by 1

CJNE R3,#00H,START ; If 255 bytes are not sent return to the

; label START



Writing message on LCD display

This example uses the m ost frequently used type of LCD which dis plays text in two lines with 16 characters each. In order to save I/O ports,

only 4 pins are used for communication here. In this way each byte is transm itted in two steps: first higher then lower nible.

LCD needs to be initialized at the beginning of the program. Besides, parts of the program which repeat in the program create special

subroutines. All this may seem extremely complicated, but the whole program bas ically performs s everal sim ple operations and dis plays

Mikroelektronika Razvojni sistemi.


58/67


*************************************************************************

;* PROGRAM NAME : Lcd.ASM

;* DESCRIPRTION : Program for testing LCD display. 4-bit communication

;* is used. Program does not check BUSY flag but uses program delay

;* between 2 commands. PORT1 is used for connection

;* to the microcontroller.

;************************************************************************

;BASIC DIRECTIVES

$MOD53

$TITLE(LCD.ASM)

$PAGEWIDTH(132)

$DEBUG

$OBJECT$NOPAGING

;Stack

DSEG AT 0E0h


59/67


Stack_Start: DS 020h

Start_address EQU 0000h

;Reset vectors

CSEG AT 0

ORG Start_address

JMP Inic

ORG Start_address+100h

MOV IE,#00 ; All interrupts are disabled

MOV SP,#Stack_Start

Inic: CALL LCD_inic ; Initialize LCD

;*************************************************

;* MAIN PROGRAM

;*************************************************

START: MOV A,#80h ; Next character will appear on the first

CALL LCD_status ; location in the first line of LCD display.

MOV A,#'M' ; Display character M.

CALL LCD_putc ; Call subroutine for character transmission.

MOV A,#'i' ; Display character i.CALL LCD_putc

MOV A,#'k' ; Display character k.

CALL LCD_putc

MOV A,#'r' ; Display character r.

CALL LCD_putc

MOV A,#'o' ; Display character o.

CALL LCD_putc

MOV A,#'e' ; Display character e.CALL LCD_putc

MOV A,#'l' ; Display character l.

CALL LCD_putc

MOV A,#'e' ; Display character e.
http://pdfcrowd.com/http://pdfcrowd.com/redirect/?url=http%3a%2f%2fwww.mikroe.com%2fchapters%2fview%2f69%2fchapter-6-examples%2f&id=ma-130201200047-f3d925f4http://pd

Www Mikroe Com Chapters View 69 Chapter 6 Examples

Documents

Transcript of Www Mikroe Com Chapters View 69 Chapter 6 Examples