AD8303

REV. 0

–14–

;AD8303.ASM

;

;

This subroutine loads an AD8303 shift register with a 12-bit

;

DAC value, and transfers the value to DAC A or DAC B.

;

The DAC value is stored at location DAC-VAL1 (MSB) and DAC_VAL0 (LSB)

;

The DAC address (A or B) is stored at DAC_ADDR, (b0=0 for A, b1=0 for B)

;

;

Primary controls

$MOD51

$TITLE(AD8303 Interface, Using the Serial Port in Mode 0)

;

;

Variable declarations

;

PORT1

DATA

90H

;SFR register for port 1

DAC_VAL0

DATA

40H

;LSBs of 12-bit DAC Value

DAC_VAL1

DATA

41H

; MSBs of DAC Value

DAC_ADDR

DATA

42H

;DAC address, format is:

; 1,1,1,1,1,1,LDB,LDA

;

Set bit low to select DAC

LOOPCOUNT

DATA

43H

;Count loops for byte swap

SHIFTREG

DATA

44H

;Shift reg. for byte swap

SENDBYTE

DATA

45H

; Destination reg. for SR

;

ORG

100H

;arbitrary starting address

DO_8303:

CLR

SCON.7

;set serial

CLR

SCON.6

;

data mode 0

CLR

SCON.5

;Clr SM2 for mode 0

CLR

SCON.1

;Clr the transmit flag

MOV

SHIFTREG,DAC_VAL1

;Get Most Significant Byte

ACALL

SEND_IT

;

send to AD8303

MOV

SHIFTREG,DAC_VAL0

;Get Least Significant Byte

ACALL

SEND_IT

;

send it to the AD8303

MOV

A,PORT1

;Get I/O port contents

ANL

A,DAC_ADDR

;Clr LDA/LDB, other bits unchanged

MOV

PORT1,A

;Send to I/O port

ORL

A,#00000011B

;Set LDA and LDB high

MOV

PORT1,A

;Send to I/O port

RET

;Done

;

;Convert the byte to LSB-first format and send it to the AD8303

SEND_IT:

MOV

LOOPCOUNT,#8

;Shift 8 bits

BYTESWAP:

MOV

A,SHIFTREG

;Get source byte

RLC

A

;rotate MSB to carry

MOV

SHIFTREG,A

;Save new source byte

MOV

A,SENDBYTE

;get destination byte

RRC

A

;Move carry into MSB

MOV

SENDBYTE,A

;Save

DJNZ

LOOPCOUNT,BYTESWAP

;Done?

MOV

SBUF,SENDBYTE

;Send the byte

SEND_WAIT:

JNB

SCON.1,SEND_WAIT

;Wait until 8 bits are send

CLR

SCON.1

;Clear the serial flag

RET

;Done

END

Figure 35. Software Listing for the AD8303-80CL51 Interface