Mitsubishi Motors DS5000TK - Manual (Page 157)

USER’S GUIDE
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OPEN: LCALL CLOSE ;Make sure it is closed.
MOV B,#4 ;Set pattern period count.
MOV A,#0C5H ;Load first byte of pattern.
OPENA: LCALL WBYTE ;Send out the byte.
XRL A,#0FFH ;Generate next pattern byte.
LCALL WBYTE ;Send out the byte.
SWAP A ;Generate next pattern byte.
DJNZ B,OPENA ;Repeat until 8 bytes sent.
RET ;Return.
;
;********************************
;*** SUBROUTINE TO CLOSE THE RTC
;********************************
;
; This subroutine insures that the registers of the timekeeper
; are closed by executing 9 successive reads of the date and time
; registers. The subroutine returns with both the accumulator
; and the B register modified.
;
CLOSE: MOV B,#9 ;Set up to read 9 bytes.
CLOSEA: LCALL RBYTE ;Read a byte.
DJNZ B,CLOSEA ;Loop for 9 byte reads.
RET ;Return.
;
;***********************************
;*** SUBROUTINE TO READ A DATA BYTE
;***********************************
;
; This subroutine performs a “context switch: to the CE2 data
; space and then reads one byte from the timekeeping device.
; Then it switches back to the CE1 data space and returns
; the byte read in the accumulator, with all other registers
; unchanged.
;
RBYTE: PUSH DPL ;Save the data
PUSH DPH ; pointer on stack.
PUSH MCON ;Save MCON register.
ORL MCON,#4 ;Switch to CE2.
PUSH B ;Save the B register.
MOV DPL,#4 ;Set up for data input.
MOV DPH,#0 ;Set high address byte.
MOV B,#8 ;Set the bit count.
LI: PUSH ACC ;Save the accumulator.
MOVX A,@DPTR ;Input the data bit from the RTC into
; ACC.7.
RLC A ;Move it to carry.
POP ACC ;Get the accumulator.
RRC A ;Save the data bit.
DJNZ B,LI ;Loop for a whole byte.
POP B ;Restore the B register.
POP MCON ;Restore the MCON register.