function-generation-report

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ES C263: Microprocessor Programming & Interfacing

Design Assignment Report

By

Nikhil R 2007A8PS028P

Sharva Kant 2007A8PS029P

R Srinivas 2007A8PS030PK Pavan Kumar Reddy 2007A8PS035P

Group No: 58

April 2009

Birla Institute of Technology & Science, Pilani


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1 | MuP Design Assignment

Table of Contents

Problem Statement .................................................................................................................... 2

Hardware Devices Used ............................................................................................................. 3

System Description .................................................................................................................... 4

Microprocessor ...................................................................................................................... 4

Memory .................................................................................................................................. 4I/O Interfacing Using 8255 ..................................................................................................... 5

I/O Map For 8255 ................................................................................................................... 5

Switches ................................................................................................................................. 6

4 Digit, 7-Segment LED display .............................................................................................. 6

DAC Controlled Function Generator ...................................................................................... 7

Software Implementation .......................................................................................................... 9

Assumptions ........................................................................................................................... 9

Algorithm ............................................................................................................................. 10

Assembly Level Program of complete implementation ...................................................... 11


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Problem Statement

Problem (P17): Frequency Generation

Description:This system is used to generate a Sine/ Triangular/ Square waveform of

Frequencies ranging from 10 Hz to 99 KHz. Voltage is between 0-10V.

Sample Operation Algorithm: To generate a Square waveform of frequency 94.35 KHz, the

user has to press Square, followed by 10K Key9 times; 1K Key4, times; 100 Key, 3 times

and 10 Key, 5 times.

When Generateis pressed, the square waveform of that frequency will be generated. If theuser wants to change the waveform into a sinusoidal one, he just has to press Sine.

SIne Tri Square

10K

1K

100

10

Generate

O/P


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Hardware Devices Used

1. INTEL 8086 : Microprocessor2. Crystal : 4 MHz Crystal3. 74LS373 (3) : 8-bit address latches- address bus4. 74LS244 : 3-state buffer- control bus5. 74LS245 (2) : 8-bit data buffers- data bus6. 2708 (2) : 1K, 8 bit EPROM7. 6116 (2) : 2K, 8 bit SRAM8. 82C55 : Programmable Peripheral Interface9. DAC0830 : 8-Bit P Compatible, Double-Buffered D to A Converters10. LMH74153 : 4:1 MUX11.Gates : AND, NAND & OR gates.12.Push Buttons (8) : For inputs13. 4- Digit 7-Segment Display14.7447 : BCD to 7-Segment Converter.15.LM392, LM394, LF351, 2N3810 : Oscillators and transistors for function

generation circuit


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System Description

This Microprocessor based Function Generator consists of the following broad subsystems.

Microprocessor Memory

o ROMo RAM

I/O Devices Interfaced to a Programmable Peripheral Interfaceo Switcheso 4 Digit, 7-Segment LED displayo DAC controlled function generator

Microprocessor

The system utilizes a standard INTEL 8086 microprocessor. The microprocessor runs on

4MHz crystal.

Memory

The memory consists of 2KB of EPROM to store the code and 4KB of SRAM to store data

during the execution. The address maps for the memory are as below.

Device A1 9 A18 A17 A16 A15 A14 A13 A12 A11 A10 A9 A8 A7 A6 A5 A4 A3 A2 A1 A0

2708

FF800H 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0

FFFFFH 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

6116

00000H 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

007FFH 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1

00800H 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0

00FFFH 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 1


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I/O Interfacing Using 8255

A programmable peripheral interface (8255) is used to interface all input and output devices

to the microprocessor.

I/O Map For 8255

Base Address: 80H

Its is I/O mapped I/O System

The addresses of the ports are as follows:

PORT of 8255 Address

PORT A 80H

PORT B 82H

PORT C 84H

Control Register 86H

Data lines: D0-D7 data lines of the microprocessor (as it is connected in even bank)

Port Specification:

Group A: Mode 0

Group B: Mode 0

Port A: Input

Port B: Output

Port C: Output

Hence, the control word is

1 0 0 1 0 0 0 0

or 90H, which is written to the control register.


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Port Ais used for the input. The 8 input buttons are connected to the 8 pins of PORT A

through a resistor and grounded.

Port Bis used to give the data (regarding frequency) to the DAC.

PORT C: 2 pins are required to select the appropriate output waveform. Two pins arerequired to select one of the four seven-segment displays at a time to display by scanning.

By setting and resetting the pins using Bit Set Reset (BSR), this can be achieved. The

remaining four bits of PORT C is used to give the BCD number to be displayed on the LED

display.

Address Map

Hex A15 A 1 4 A 1 3 A 1 2 A 1 1 A 1 0 A 9 A 8 A 7 A 6 A 5 A 4 A 3 A 2 A 1 A 0

0080H 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0

0082H 0 0 0 0 0 0 0 0 1 0 0 0 0 0 1 0

0084H 0 0 0 0 0 0 0 0 1 0 0 0 0 1 0 0

0086H 0 0 0 0 0 0 0 0 1 0 0 0 0 1 1 0

Switches

We need 8 buttons to select the following functions: 10 Hz, 100 Hz, 1 KHz, 10 KHz, Sine, Tri,Square & Generate. This is implemented by using 8 push buttons, one each attached to the

8 pins of PORT A in 8255. The buttons are so connected through a resistor and ground, such

that on press, the corresponding pin is pulled down to a Logic Low. All lines from the input

port are NANDed together and connected to the external interrupt INTR of the

microprocessor. The service routine for INTR has been interfaced at FFh.

4 Digit, 7-Segment LED display

The frequency typed by the user is displayed on 4-Digit, 7-Segment LED display. The four

digits are displayed by the process of Scanning in which only one of displays is lit at a time.

The digits to be displayed are displayed in each display for a short period of time (~ 2ms)

and the entire process is repeated over and over again to give an impression of static display

(due to persistence of vision)

PC0- PC3of 8255 is used to give a BCD value to a BCD to 7-Segment converter IC (7447). The

pins PC4 & PC5are used to select on of the four displays at any point of time.


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If D is the data sent to the DAC, the frequency of signal received in the output is given by

- where C, the value of capacitance was found to be 0.5 nF for the current purpose.The circuit has 3 outputs, O1, O2 & O3. Depending on the form of the wave selected by the

user, one of three outputs is selected using a multiplexer.

The pins PC6 & PC7are used to select the required output signal and provide the output.

This is done using a 4:1 MUX.


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Software Implementation

Assumptions

The following assumptions were made in order to develop the software for the system.

At the location FFFF0H, where the instruction pointer points on RESET ofmicroprocessor, there exists a JUMP statement leading to the start of the code.

The user gives sufficient time between two successive key presses, enough toperform all operations associated with a particular key press. The software however

is designed to handle debounce.

The user can only increase the frequency and never decrease. If he/she requires alower value of frequency, the system needs to shut down and restarted.

The maximum frequency of signal to be generated s 99.99 khz and user does notenter anything above this value.

The interrupt vector corresponding to external interrupt is FFh and is supplied to themicroprocessor externally.


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Algorithm

1. The frequency to be input from the user is stored as a 4-digit BCD value in memory.The form type as well as the data to be sent to DAC is also stored in the memory. All

the values are initially zero.

2. The processor now continuously displays the 4 digit BCD value stored in memory onthe 7-segment LED displays by the process of scanning. This display is made inside an

infinite loop.

3. On key press, the external interrupt is triggered and the corresponding interruptservice routine (ISR) at FFh is called.

4. In the ISR, the value of PORTA of 8255 is Input and compared with values todetermine which key has been pressed.

a. If the key was any of the multiplier keys, the frequency stored in the memoryis correspondingly multiplied.

b. If the key was a form selector key, the form in the memory is correspondinglyupdated.

c. If the key was the Generate Key, then the frequency in memory is convertedto the 8-bit equivalent to be sent to the DAC, the value is Output to PORTB of

8255 and the pins PC6 & PC7 are set/reset based on the form factor.

The control is returned back to the mainline program after a debounce period,

where the frequency continues to be displayed while the output remains as the

required signal as the outputs in 8255 are latched.


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Assembly Level Program of complete implementation

.model small

.data

frequency dw 0000h

form db 00h

dacdata db 00h

.code

.startup

;initializing the PPI

mov al, 90h

OUT 86h, al

;initializing the data to DAC and waveform to 0

mov al, 00h

out 82h, al ;PORT B is set to 0

out 84h, al ;PORT c is set to 0

loop:

mov ax, frequency

;isolating each digit of the BCD frequency

mov cx, 04h

mov bx, ax

shl ah, cx

and bh, 0Fh

shl al, cx

and bl, 0Fh

;ah, bh, al, bl now have the four digits in the same order

; outputting the frequency to 7-segment LED display by method of scanning

out 84h, ah ;sets the first 4 bits of PORT C to the value contained in ah (first digit)

mov ch, 08h ;BSR control word to reset 4th bit

out 86h, ch

mov ch, 0Ah ;BSR control word to reset 5th bit

out 86h, ch

CALL delay


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out 84h, bh ;sets the first 4 bits of PORT C to the value contained in bh (second digit)

mov ch, 09h ;BSR control word to set 4th bit

out 86h, ch

mov ch, 0Ah ;BSR control word to reset 5th bit

out 86h, ch

CALL delay

out 84h, al ;sets the first 4 bits of PORT C to the value contained in al (third digit)

mov ch, 08h ;BSR control word to reset 4th bit

out 86h, ch

mov ch, 0Bh ;BSR control word to set 5th bit

out 86h, ch

CALL delay

out 84h, bl ;sets the first 4 bits of PORT C to the value contained in bl (fourth digit)

mov ch, 09h ;BSR control word to set 4th bitout 86h, ch

mov ch, 0Bh ;BSR control word to set 5th bit

out 86h, ch

CALL delay

jmp loop ;cause the display to happen in an infinite loop

.exit

; external interrupt service routine

isr(int FFh)

in al, 80h

cmp al, FEh ;chk if the 10 button was pressed

jz ten

cmp al, FDh ;chk if the 100 button was pressed

jz hundred

cmp al, FBh ;chk if the 1K button was pressed

jz onek

cmp al, F7h ;chk if the 10K button was pressed

jz tenk

cmp al, EFh ;chk if the sine button was pressed

jz sine

cmp al, DFh ;chk if the tri button was pressed


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jz tri

cmp al, BFh ;chk if the square button was pressed

jz square

cmp al, 7Fh ;chk if the generate button was pressed

jz generate

ten: ;adds 10 hertz to frequency

mov bx, frequency

add bl, 01h

mov frequency, bx

jmp finish

hundred: ;adds 100 hertz to frequencymov bx, frequency

add bl, 10h

mov frequency, bx

jmp finish

onek: ;adds 1K hertz to frequency

mov bx, frequency

add bh, 01h

mov frequency, bx

jmp finish

tenk: ;adds 10K hertz to frequency

mov bx, frequency

add bh, 10h

mov frequency, bx

jmp finish

sine: ;sets the form byte to 00h if the sine button was pressed

mov form, 00hjmp finish

tri: ;sets the form byte to 01h if the tri button was pressed

mov form, 01h

jmp finish

square: ;sets the form byte to 02h if the square button was pressed

mov form, 02h

jmp finish


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generate: ;performs necessary computations to calculate D to DAC, sets the o/p select,

outs the D to DAC

mov ax, frequency

;unpacking BCD and converting to binary

mov bl, al

and bl, 0Fh

mov cl, 04h

shr al, cl

mov bh, al

mov dl, ah

and dl, 0Fh

mov cl, 04h

shr ah, clmov dh, al

mov al, 10

mul bh

add ax, bl

mov bx, ax

mov al, 100

mul dl

add bx, ax

mov al, 1000

mul dh

add bx, ax

;bx has the frequency*100 stored in it

mov ax, 256

mul bx

mov cx, 10000div cx

;now ax has a value between 0-255 corresponding to the frequency

out 82h, al ; outs the frequency to the DAC and latches it

cmp form, 00h

jz sineout

cmp form, 01hjz triout


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