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AD8803

Octal 8-Bit TrimDAC with Power Shutdown

Analog Devices 

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

DAC_VALUE

DATA

40H

DAC_ADDR

DATA

41H

SHIFT1

DATA

042H

SHIFT2

DATA

043H

SHIFT_COUNT

DATA

44H

;

ORG

100H

DO_8801:

CLR

SCON.7

CLR

SCON.6

CLR

SCON.5

CLR

SCON.1

ORL

PORT1.1,#00001110B

CLR

PORT1.1

MOV

SHIFT1,DAC_ADDR

ACALL

BYTESWAP

MOV

SBUF,SHIFT2

ADDR_WAIT:

JNB

SCON.1,ADDR_WAIT

CLR

SCON.1

MOV

SHIFT1,DAC_VALUE

ACALL

BYTESWAP

MOV

SBUF,SHIFT2

VALU_WAIT:

JNB

SCON.1,VALU_WAIT

CLR

SCON.1

SETB

PORT1.1

RET

;

BYTESWAP:

MOV

SHIFT_COUNT,#8

SWAP_LOOP:

MOV

A,SHIFT1

RLC

A

MOV

SHIFT1,A

MOV

A,SHIFT2

RRC

A

MOV

SHIFT2,A

DJNZ

SHIFT_COUNT,SWAP_LOOP

RET

END

;SFR register for port 1

;DAC Value

;DAC Address

;high byte of 16-bit answer

;low byte of answer

;

;arbitrary start

;set serial

; data mode 0

;clr transmit flag

;/RS, /SHDN, /CS high

;set the /CS low

;put DAC value in shift register

;

;send the address byte

;wait until 8 bits are sent

;clear the serial transmit flag

;send the DAC value

;

;

;wait again

;clear serial flag

;/CS high, latch data

; into AD8801

;Shift 8 bits

;Get source byte

;Rotate MSB to carry

;Save new source byte

;Get destination byte

;Move carry to MSB

;Save

;Done?

Listing 1. Software for the 8051 to AD8801/AD8803 Serial Port Interface

–10–

REV. A

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