Datasheet

REV. A
–10–
AD8801/AD8803
;
; This subroutine loads an AD8801/AD8803 DAC from an 8051 microcomputer,
; using the 8051’s serial port in MODE 0 (Shift Register Mode).
; The DAC value is stored at location DAC_VAL
; The DAC address is stored at location DAC_ADDR
;
; Variable declarations
;
PORT1 DATA 90H ;SFR register for port 1
DAC_VALUE DATA 40H ;DAC Value
DAC_ADDR DATA 41H ;DAC Address
SHIFT1 DATA 042H ;high byte of 16-bit answer
SHIFT2 DATA 043H ;low byte of answer
SHIFT_COUNT DATA 44H ;
;
ORG 100H ;arbitrary start
DO_8801: CLR SCON.7 ;set serial
CLR SCON.6 ; data mode 0
CLR SCON.5
CLR SCON.1 ;clr transmit flag
ORL PORT1.1,#00001110B ;/RS, /SHDN, /CS high
CLR PORT1.1 ;set the /CS low
MOV SHIFT1,DAC_ADDR ;put DAC value in shift register
ACALL BYTESWAP ;
MOV SBUF,SHIFT2 ;send the address byte
ADDR_WAIT: JNB SCON.1,ADDR_WAIT ;wait until 8 bits are sent
CLR SCON.1 ;clear the serial transmit flag
MOV SHIFT1,DAC_VALUE ;send the DAC value
ACALL BYTESWAP ;
MOV SBUF,SHIFT2 ;
VALU_WAIT: JNB SCON.1,VALU_WAIT ;wait again
CLR SCON.1 ;clear serial flag
SETB PORT1.1 ;/CS high, latch data
RET ; into AD8801
;
BYTESWAP: MOV SHIFT_COUNT,#8 ;Shift 8 bits
SWAP_LOOP: MOV A,SHIFT1 ;Get source byte
RLC A ;Rotate MSB to carry
MOV SHIFT1,A ;Save new source byte
MOV A,SHIFT2 ;Get destination byte
RRC A ;Move carry to MSB
MOV SHIFT2,A ;Save
DJNZ SHIFT_COUNT,SWAP_LOOP ;Done?
RET
END
Listing 1. Software for the 8051 to AD8801/AD8803 Serial Port Interface