Microcontroller User's Guide

USER’S GUIDE
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POP DPH ;Restore the data
POP DPL ; pointer from stack.
RET ;Return.
;
;************************************
;*** SUBROUTINE TO WRITE A DATA BYTE
;************************************
;
; This subroutine performs a “context switch” to the CE2 data
; space and then writes one byte from the accumulator to the
; timekeeping device. Then it switches back to the CE1 data
; space and returns with all registers unchanged.
;
WBYTE: PUSH DPL ;Save the data
PUSH DPH ; pointer on stack.
PUSH MCON ;Save the MCON register.
ORL MCON,#4 ;Switch to CE2.
PUSH B ;Save the B register.
MOV DPH,#0 ;Set high address byte.
MOV B, #8 ;Set the bit Count.
LO: PUSH ACC ;Save the accumulator.
ANL A, #1 ;Set up bit for output.
MOV DPL,A ;Set address to write bit.
MOVX A, @DPTR ;Output the data bit.
POP ACC ;Restore the accumulator.
RR A ;Position next bit.
DJNZ B, LO ;Loop for a whole byte.
POP B ;Restore the B register.
POP MCON ;Restore the MCON register.
POP DPH ;Restore the data
POP DPL ; pointer from stack.
RET ;Return.
;
;****************
; END OF PROGRAM
;****************
;
END ;End of program.