The PIC Microcontrollers

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The PIC Microcontrollers

• The PIC microcontroller was designed by General
  Instruments
• The PIC microcontroller is a complete computer
  contained within one chip
• It contains the CPU, memory and IO devices all in
  one chip
• The microcontroller contains many IO ports such
  as PORTA, B, C, D, E
• It contains also timers, analog to digital
  converter, USART
• This make this device an ideal solution for small
  project

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MEMORY ORGANIZATION

• There are three memory blocks in each of the
  PIC16F87A devices
• The program memory
• The data memory
• Stack memory
• The program memory and data memory have separate
  buses which allows concurrent access

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Program Memory Organization

• The PIC microcontroller contains many internal
  registers to control its operation
• One of these registers is the program counter
• The program counter is 13-bits wide in the
  16F877A microcontrollers
• This limits the program memory space to 2138k
  words14 bits of flash program memory
• When the microprocessor is first powered up it
  starts execution at memory location 0000H
• When an interrupt occurs the microprocessor goes
  to memory location 0004H

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Data Memory Organization

• The data memory is partitioned into multiple
  banks which contains
• The General Purpose Registers
• The Special Function Registers

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Data Memory Organization

• A given bank is selected by bits RP1 (Statuslt6gt)
  and RP0 (Statuslt5gt) according to the table shown
  below
• These two bits are located in the status register
  which is equivalent to the flag register found in
  the 8086

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SPECIAL FUNCTION REGISTERS

• The Special Function Registers are registers used
  by the CPU and peripheral modules for controlling
  the desired operation of the device
• These registers are shown in the attached sheets
• The most important registers will be discussed
  next

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Status Register

• The Status register contains the flag bits, reset
  status and the bank select bits for data memory

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OPTION_REG Register

• This register contains various control bits to
  configure
• the TMR0 prescaler/WDT postscaler (single
  assignable
• register known also as the prescaler), the
  external
• INT interrupt, TMR0 and the weak pull-ups on PORTB

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INTCON Register

• This register is responsible controlling hardware
  interrupts
• The GIE (bit 7) is responsible for enable or
  disable of all interrupts in the system
• If GIE is 1 then all interrupts will be enabled
  otherwise all interrupts will be disabled
• A complete description of these interrupts will
  be provided in the next slide

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PIE1 Register

• The PIE1 register contains the individual
  enable/disable bits for the peripheral interrupts
• Peripherals are
• the analog to digital converter
• USART receiver
• USART transmitter
• Synchronous Serial Port
• Timer1
• Timer2

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PIR1 Register

• When an interrupt is generated, it is important
  to know which one of the above mentioned
  peripherals generates the interrupt
• This can be done by inspecting the state of the
  PIR1 register which contains several flag bits
  corresponds to each peripheral
• If an interrupt occurs, then the program can test
  the flags located in this register to determine
  which device generated the interrupt
• A complete explanation for this register is
  provided in the next slide

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PCON Register

• The Power Control (PCON) register contains flag
  bits to allow differentiation between a Power-on
  Reset (POR), a Brown-out Reset (BOR), a Watchdog
  Reset (WDT) and an external MCLR Reset