8051 I/O EXPANSION EXAMPLES The following source code and schematic show how to expand the 8051 I/O using common shift register chips. ; ----------------------------------------------------------------------- ; I/O EXPANSION ROUTINES FOR 8051 FAMILY MICROCONTROLLERS ; WRITTEN BY GARY PEEK ; ----------------------------------------------------------------------- ; USE THE READINIT AND WRITEINIT ROUTINES DURING INITIALIZATION ; USE THE READ8 AND WRITE8 ROUTINES WHEN USING ONLY ONE CHIP (8 BITS) ; USE THE READ16 AND WRITE16 ROUTINES WHEN USING TWO CHIPS (16 BITS) ;SAMPLE PORT BIT EQUATES CLOCK BIT P1.7 ;MICROCONTROLLER OUTPUT STROBE BIT P1.6 ;MICROCONTROLLER OUTPUT DATAOUT BIT P1.5 ;MICROCONTROLLER OUTPUT LOADSHIFT BIT P1.4 ;MICROCONTROLLER OUTPUT DATAIN BIT P1.3 ;MICROCONTROLLER INPUT ; 4094 SHIFT REGISTER OUTPUT ROUTINES WRITEINIT: ;PINS USED FOR OUTPUT SHIFT REGISTER CLR CLOCK ;INITIALIZE LOW FOR A HIGH GOING CLOCK CLR STROBE ;INITIALIZE LOW FOR A HIGH GOING LATCH RET ;DATAOUT DOES NOT NEED TO BE INITIALIZED ;ENTER WITH OUTPUT BYTE IN ACCUMULATOR WRITE8: MOV B,#8 ;NUMBER OF BITS TO DO WR8L: RLC A ;ROTATE BIT 7 INTO CARRY MOV DATAOUT,C ;PUT CARRY INTO OUTPUT BIT SETB CLOCK ;CLOCK DATA THROUGH CHIP CLR CLOCK DJNZ B,WR8L ;LOOP UNTIL ALL BITS DONE SETB STROBE ;LATCH DATA INTO OUTPUT REGISTER CLR STROBE RET ;ENTER WITH HIGH BYTE IN REGISTER B ;ENTER WITH LOW BYTE IN ACCUMULATOR WRITE16:PUSH ACC ;SAVE LOW BYTE FOR NOW MOV A,B ;PUT HIGH BYTE IN ACC, SHIFT IT FIRST CALL CLKOUT ;CLOCK BITS THROUGH THE CHIPS POP ACC ;RESTORE THE LOW BYTE CALL CLKOUT ;CLOCK BITS THROUGH THE CHIPS RET CLKOUT: MOV B,#8 ;NUMBER OF BITS TO DO CLKOL: RLC A ;ROTATE BIT 7 INTO CARRY MOV DOUT,C ;PUT CARRY INTO OUTPUT BIT SETB CLOCK ;CLOCK DATA THROUGH CHIP CLR CLOCK DJNZ B,CLKOL ;LOOP UNTIL ALL BITS ARE DONE SETB STROBE ;LATCH DATA INTO OUTPUT REGISTER CLR STROBE RET ; 74165 SHIFT REGISTER INPUT ROUTINES READINIT: ;PINS USED FOR INPUT SHIFT REGISTER CLR CLOCK ;INITIALIZE LOW FOR A HIGH GOING CLOCK CLR LOADSHIFT ;INITIALIZE LOW FOR NORMAL "LOAD" FUNCTION SETB DATAIN ;INITIALIZE HIGH SO IT CAN BE AN INPUT RET READ8: MOV B,#8 ;DO 8 BITS SETB LOADSHIFT ;SET CHIP TO BEGIN SHIFTING DATA OUT RD8L: SETB CLOCK ;CLOCK DATA TO THE OUTPUT PIN CLR CLOCK MOV C,DATAIN ;PUT INPUT BIT INTO CARY RRC A ;ROTATE CARRY INTO BIT 7 DJNZ B,RD8L ;LOOP UNTIL ALL BITS ARE DONE CLR LOADSHIFT ;SET CHIP TO LOAD DATA AGAIN RET ;EXIT WITH INPUT BYTE IN ACCUMULATOR READ16: SETB LOADSHIFT ;SET CHIPS TO BEGIN SHIFTING DATA OUT CALL CLKIN ;CLOCK BITS THROUGH CHIPS PUSH ACC ;SAVE LOW BYTE JUST READ FOR NOW CALL CLKIN ;CLOCK BITS THROUGH CHIPS MOV B,A ;STORE HIGH BYTE POP ACC ;RESTORE LOW BYTE CLR LOADSHIFT ;SET CHIP TO LOAD DATA AGAIN RET ;EXIT WITH HIGH BYTE IN REGISTER B ;EXIT WITH LOW BYTE IN ACCUMULATOR CLKIN: MOV B,#8 ;DO 8 BITS CLKIL: SETB CLOCK ;CLOCK DATA TO THE OUTPUT PIN CLR CLOCK MOV C,DATAIN ;PUT INPUT BIT INTO CARY RRC A ;ROTATE CARRY INTO BIT 7 DJNZ B,CLKIL ;LOOP UNTIL ALL BITS ARE DONE RET ;EXIT WITH BYTE IN ACCUMULATOR (C) Copyright 1997 - 2008 by Vault Information Services LLC. All Rights Reserved. Information provided "as-is" without warranty. Please see details. Contact us for usage and copy permission.