PIC Microcontroller I/O Ports and Digital I/O Operations, Slides of Computer Architecture and Organization

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PIC Peripherals^ Digital I/O

PIC16 MCU Peripherals • Digital I/O• Timers• A/D converter• Comparator• Parallel slave port• Interrupts

I/O pin operation CPU Data Bus^

DataDirectionTri-stateLatch^ OutputEnableOutput OutputCurrentDataDriverLatch InputDataLatch Write TRIS bit Write data bitRead databit Analogue inputmultiplexer The pin can be set for input or output data transfer

16F877 I/O Ports • The 16F877 has the following digital I/Oports available:• Port A RA0–RA^

6 bits

• Port B^ RB0–RB

8 bits

• Port C^ RC0–RC

8 bits

• Port D^ RD0–RD

8 bits

• Port E^ RE0–RE

3 bits

• Total digital I/O available

33 pins

TRISx (Low Level Prog.) • Used to Control Direction of PORTx – Input or Output– No Bidirectional Use Without Changing TRISXBack and Forth • Must Set TRISx^

Before^ Using PORTx

• TRISx = 0^
  

PORTx Is OUTPUT (0 = O)

• TRISx = 1^
  

PORTx Is INPUT (1 = I)

Example MOVLW 0x0^ ;WREG = 0MOVWF TRISB^ ;make PORTB output

L1^ MOVLW^

0x55^ ;WREG = 55HMOVWF PORTB^ ;put 55H

on PORTB CALL^ DELAYMOVLW^ 0xAA

;WREG = AAH MOVWF^ PORTB

;put AAH^

on PORTB CALL^ DELAYGOTO^ L^

;^ Loop

PORTA

• Only 7 Pins (RA0-RA6)• RA6 is Dual-Use^ – Not Available If Using a Crystal Oscillator forFrequency Provision • NOTE: You Still Write All 8 Bits to TRISAand PORTA^ – Excess Data Goes in the Bit Bucket, So BeCareful!

PORTB

• All 8 Pins (RB0-RB7)• Set By TRISB• PORTA and PORTB Have a Dual Role^ – Multiplexes an A/D Converter (Later) • DO NOT USE PORT A and PORTB WhenYou Need the A/D Converter

PORTD

• 8 Pins• Uses TRISD• BUT, PORTD Has Dual Use^ – Later

PORTE

• Only 3 Pins!• Uses TRISE to Set Direction• Also Has Alternate Functions

Pipeline for Read Followed by Write I/O

Port Status on Reset • Defaults – TRISx = 0xFF– All Ports Become INPUT Ports

Bit-Oriented Instructions inAssembly • BSF^ Bit^ Set^ fileReg• BCF^ Bit^ Clear

fileReg

• BTG^ Bit

Toggle fileRe

g

• BTFSC^ Bit

Test^ fileReg,

Skip if^ Clear

• BTFSS^ Bit

Test^ fileReg,

Skip if^ Set

• In CCS C compiler, all this Assembly storyis just part of few C lines!