PIC MICROCONTROLLER PROGRAMMING -...

E n g . S a r e e h y _ A h m e d A k o u r @ Y a h o o . c o m | E n g . A h m e d A k o u r

PR

OG

RA

MM

ING

En

g.A

hm

ed

Ako

ur

PIC

MIC

RO

CO

NT

RO

LL

ER

P

RO

GR

AM

MIN

G

PIC MICROCONTROLLER PROGRAMMING

What is the microcontroller?


Harvard Vs Von Neumann Architecture

The von neumann Architecture uses a single memory (program memory & data memory)

Connected to the CPU by using a single address bus ,a single data bus,and single control

bus.

The Harvard Architecture uses different memories for data and program connected to the

CPU by an instruction address bus,a data address bus,an instruction bus, a data bus ,an

instruction control bus,and data control bus.


Microcontroller (μC) Vs microprocessor (μP).

Figure below shows the internal architecture of a typical µC system, and its equivalent

µP system, note that in the µC side, all devices are packaged in the same chip, in contrast of

µP system that each block is considered a stand-alone device.


PIC16 identification: PIC is generally assumed to mean Peripheral Interface Controller, it comes with a

variety of families; PIC10 and PIC12 (Base-line), PIC16 (Mid-range), PIC17 (High-end),

PIC18 (enhancement), Finally PIC24 and dsPIC. Here we will deeply look at PIC16

family. PIC16F84A is our interest MCU in this family.

PIC16F877A: Is a 40 pin chip, operating at a frequency up to 20MHz, it has five I/O ports

A(6),B(8),C(8),D(8),E(3) mapping to 33 pins, the following points highlight the

most important features:

1- 8Kbx 14 words Flash Program memory space.

2- 368 x 8 Bytes of DATA Memory (RAM).

3- 256 x 8 Bytes of EEPROM DATA Memory.

4- Five I/O PORTS.

5- Wide operating frequency DC-20MHz.

6- Wide operating voltage 2.0v – 5.5v.

7- Three timers with different capabilities. 8- Two Capture\Compare\PWM modules (CCP). 9- 10,000 erase/write cycles Enhanced FLASH Program memory typical.

10- 10,000,000 typical erase/write cycles EEPROM Data memory typical.

11- EEPROM Data Retention > 40 years.

12- 15 kinds of interrupts. 13- RS-232, I2C, and SPI interfaces (USART, MSSP). 14- current sink/source :

- 25 mA sink max. per pin.

- 25 mA source max. per pin.


MEMORY ORGANIZATION: There are two memory blocks in the PIC16F877A.These are the program memory and the data memory. Each block has its own bus, so that access to each block can occur during the same oscillator cycle.

Program memory:

The PIC16F877A has a 13-bit program counter capable of addressing a 8K x 14

program memory space. The RESET vector is at 0000h and the interrupt vector is at

0004h .

Program Counter (PC): is CPU register where adresses of instructions are

stored.every time that the CPU looks for an instruction in the memory,the PC is

increased,pointing to the following instruction.in an instant of time the PC

contains the adress of the instruction that will be excuted next.


Data Memory(RAM):

Data Memory is devided into four pages called

Banks(Bank0,Bank1,Bank2,Bank3).

Each Bank has 128 locations (addresses or registers) .including the General

Purpose Registers(GPRs) and the Special Function Registers(SFRs). Bits RP1

(Status<6>) and RP0 (Status<5>) are the bank select bits

SFRs are used to control PIC and access its peripheral modules.GPRs make up

the data memory available to the user .

Note that the GPRs addresses start from address 20h.


Program memory Data memory EEPROM

Data bus 14 bit 8 bit 8 bit

Address bus 13 bit 7 bit 8 bit

STATUS REGISTER: The STATUS register contains the arithmetic status of the ALU, the RESET status And the bank select bit for data memory.


OPTION REGISTER The OPTION register is a readable and writable register which contains various control bits to configure the TMR0/WDT prescaler, the external INT interrupt, TMR0, and the weak pull-ups on PORTB.


PINOUT:

Pic16F877A has 40 pins:

33 as i/o pins.

7 pins for biase ,oscillator and reset .

MCLR# (reset pin): pin # 1 ,this pin used to

manually reset the program execution when

it goes low (logicaly zero).

Connection:this pin is active low so it is usually connected to 5 Volt

(Vcc/Vdd) through a resistor (typical 10KΩ) to prevent any unwanted reset

during program execution.


Bias: any IC needs bias to operate. PIC 16F877A has four pins for biasing these

pins are Vdd (Pin #11,Pin #32 connected to 5 Volt) and

Vss (Pin #12,Pin #31 connected to GND).

Connection:


Oscillator: the µC needs oscillator to generate the signal necessary to

synchronize all internal operation.

PIC16F877A has two pins for oscillator these pins are pin #13

(OSC1/CLKIN) and pin #14 (OSC2/CLKOUT).

Connection:

The main oscillator in PIC Microcontroller can be internal or External

clock.

Internal Oscillator/Clock: Some of microcontrollers have an internal RC

oscillator.

- frequency up to 4 MHz.

- error 1.5%.

- 12xxx,10xxx,some of 16xxx and 18xxx series.


External Oscillators/Clock:either RC Oscillator or (crystal/cyramic)

Oscillators.

o RC Oscillator :

- Frequency up to 1MHz.

- Error 30%.

- Timing insensetive.

- Low Cost.

o Ceramic Oscillator:

- Error 0.5%.

- Robust.

- Used in remote control.

- Frequency up to 4Mhz.

o Crystal Oscillator:

- Error (0.02-0.1)%.

- Best used.

Speed Mode in Software: The type of oscillator can be selected by the

configuration bits.these also select specific modes of operation:

- LP mode: selects oscillator frequencies between (32KHz-200KHz).

- XT mode: selects oscillator frequencies between (100KHz-4MHz).

- HS mode: selects oscillator frequencies between (8MHz-20MHz).

- RC mode: when we use an external RC network as an oscillator.


I/O Pins: Pic 16F877A has 33 pins can be used as input or output. These pins are

classified to five Ports PortA (6 Pins) , PortB (8 Pins), PortA (6 Pins) and PortB (8 Pins)

And PortE(3).

Port Name Number Of Pins

PORTA 6

PORTB 8

PORTC 8

PORTD 8

PORTE 3

TOTAL 33

Configure i/o pins as Input or Output:

Each port needs two special function register:

Data direction register called TRIS (8 bit register): this

register responsible for determining which pin in the port either input

or output.

Setting any bit in this register to 1 will make the pin corresponding to

that pin is input ,while setting any bit in the register to 0 will make

the pin corresponding to that pin is output.

Eg. We want to load the following value in TrisB register.

Loading 0x03(hexadecimal) == 0b00000011(binary).

- Loading 0x03 into TRISB make pin RB0 & RB1 as an input pins and the

other pins (RB2,RB3,RB4,RB5,RB6,RB7) as an output.

- Similarly loading 0x01==0b00000001 into TRISA making the bit RA0

(bit #0) as an input pin and other pins (RA1,RA2,RA3,RA4,RA5) as an

output.

RB7 RB6 RB5 RB4 RB3 RB2 RB1 RB0

0 0 0 0 0 0 1 1

TRISB REGISTER


RA5 RA4 RA3 RA2 RA1 RA0

0 0 0 0 0 1

Data Register Called Port (8 bit register): this register responsible for writing to

the output pins or reading from input pins.

Configuration Bits: these bits allow the programmer to specify certain

aspects of microcontroller to better fit the intended application.

- These bits must be selected at the beginning of the program.

- These bits can't be changed during programming.

- These bits like fuses.

- These bits are responsible for specifying :

i. Oscillator mode.

ii. Reset parameter (watchdog timer on or off, brown out).

iii. Program memory protection.

iv. Protection of EEPROM data.

v. Power mode (3v or 5v).

Selecting the configuration bits in software:

The configuration bits must be selected at the beginning of the program by writing

the following statement

__CONFIG _XT_OSC &_LVP_OFF &_WDT_OFF &_PWRTE_ON &_CP_OFF

TRISA REGISTER


References:

1. Microcontroller fundamentals and applications with PIC, Fernando E.Valdes.

2. PIC MICROCONTROLLER,Ahmed Ihmeid.

3. PIC 16F877A datasheet ,microchip.


GOOD LUCK

ENG AHMED AKOUR

PIC MICROCONTROLLER PROGRAMMING -...

Documents

Transcript of PIC MICROCONTROLLER PROGRAMMING -...