PIC Microcontrollers PIC16F877A/PIC16F874A

PIC Microcontrollers PIC16F877A/PIC16F874A: The name PIC is referred to Peripheral Interface Controller.

Contents

What is PIC?

A family of Harvard architecture microcontrollers made by Microchip Technology.

Micro Controller : Micro Processor + Peripherals

Derived from the PIC1650 originally developed by General Instrument Microelectronics Division.

The name PIC was originally an acronym for “Programmable Intelligent Computer”.

The name PIC is referred to Peripheral Interface Controller.

It shares some common features with RISC designs

Why PIC is popular?

 low cost ,wide availability with high clock speed
 of low cost or free development tools
 Only 35 instructions to remember
 serial programming and re-programming with flash memory capability
 Its code is extremely efficient, allowing the PIC to run with typically less program memory than its larger
competitors
PIC is very small and easy to implement for non-complex problems and usually accompanies to the microprocessors as an interface

Classification of PIC Microcontrollers

Based on instruction word length

 Base-Line or low end Architectures: 12-bit Instruction Word
length (PIC10FXX,PIC12C5XX,PIC16C5X)
 Mid-Range Architectures : 14-bit Instruction Word length
(PIC16C6X,PIC16C7XX,PIC16F877X)
 High-End Architectures : 16-bit Instruction Word length
(PIC17C4x,PIC17C7xx,PIC18Cxxx, PIC18F452

Based on data length

 8 bit microcontroller (PIC1612F,PIC17F,PIC16F877)
 16 bit microcontroller(dsPIC30F,dsPIC33F, PIC24FX,PIC24H)
 32 bit microcontroller(PIC32FXX,PIC32MX)

The PIC Family: Speed

12C50X – 4MHz
12C67X – 10MHz
16F877 – 20MHz
17C4X/17C7XXX – 33MHz
18CXXX – 40MHz

Can use crystals, clock oscillators, or even an RC circuit.
Some PICs have a built in 4MHz RC clock, Not very accurate, but requires no external components!
Instruction speed = 1/4 clock speed (Tcyc = 4 * Tclk)
All PICs can be run from DC to their maximum specified speed:

Clock and Instruction Cycles

Instruction Clock

– Clock from the oscillator enters a microcontroller via OSC1 pin where internal circuit of a microcontroller divides the clock into four even clocks Q1, Q2, Q3, and Q4 which do not overlap.
– These four clocks make up one instruction cycle (also called machine cycle) during which
one instruction is executed.
– Execution of instruction starts by calling an instruction that is next in string.
– Instruction is called from program memory on every Q1 and is written in instruction register on Q4.
– Decoding and execution of instruction are done between the next Q1 and Q4 cycles. On the following diagram we can see the relationship between instruction cycle and clock of the oscillator (OSC1) as well as that of internal clocks Q1-Q4.
– Program counter (PC) holds information about the address of the next instruction.

The PIC Family: Program Memory

Technology: EPROM, FLASH, or ROM
It varies in size from one chip to another.

12C508	512	12bit instructions
16C711	1024 (1k)	14bit instructions
16F877	8192 (8k)	14bit instructions
17C766	16384 (16k)	16bit instructions

PIC16F877A Features

High Performance RISC CPU:
Only 35 single word instructions to learn
Operating speed: DC – 20 MHz clock input DC – 200 ns instruction cycle
All single cycle instructions except for program branches, which are two-cycle
PIC Memory
The PIC16F877A has an 8192 (8k) 14bit instruction program memory
368 Bytes Registers as Data Memory :
– Special Function Registers: used to control peripherals and PIC behaviors
– General Purpose Registers: used to a normal temporary storage space (RAM)
256 Bytes of nonvolatile EEPROM Peripheral Features
Timer0: 8-bit timer/counter with 8-bit prescaler
Timer1: 16-bit timer/counter with prescaler,can be incremented during Sleep via
external crystal/clock
Timer2: 8-bit timer/counter with 8-bit period register, prescaler and postscaler
Two Capture, Compare, PWM modules
Capture is 16-bit, max. resolution is 12.5 ns
Compare is 16-bit, max. resolution is 200 ns
PWM max. resolution is 10-bit
10-bit, up to 8-channel Analog-to-Digital Converter (A/D)
Synchronous Serial Port (SSP) with SPI™(Master mode) and I2C™ (Master/Slave)
Universal Synchronous Asynchronous Receiver,Transmitter (USART/SCI) with 9-bit address detection
Parallel Slave Port (PSP) – 8 bits wide with external RD, WR and CS controls
Brown-out detection circuitry for Brown-out Reset (BOR)

Peripheral Features PIC16F877a

– 5 Digital I/O Ports
– Three timer/counter modules

Timer0: 8-bit timer/counter with 8-bit pre-scaler
Timer1: 16-bit timer/counter with pre-scaler, can be incremented during SLEEP via
external crystal/clock
Timer2: 8-bit timer/counter with 8-bit period register, pre-scaler and post-scaler
– A 10-bit ADC with 8 inputs
– Two Capture, Compare, PWM modules
Capture is 16-bit, max. resolution is 12.5 ns
Compare is 16-bit, max. resolution is 200 ns
PWM max. resolution is 10-bit
– Synchronous Serial Port (SSP) with SPI™ (Master mode) and I2C™ (Master/Slave)
– Universal Synchronous Asynchronous Receiver Transmitter (USART/SCI) with 9-bit
address detection
– Parallel Slave Port (PSP) 8-bits wide, with external RD, WR and CS controls