TLV5604

2.7-V TO 5.5-V 10-BIT 3-

µS QUADRUPLE DIGITAL-TO-ANALOG CONVERTERS

WITH POWER DOWN

SLAS176A – DECEMBER 1997 – REVISED SEPTEMBER 1998

21

POST OFFICE BOX 655303

APPLICATION INFORMATION

;––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––

; Processor:

80C51

;

; Description:

;

; This program generates a differential in–phase (sine) on (OUTA–OUTB) and it’s

; quadrature (cosine) as a differential signal on (OUTC–OUTD).

;

© 1998, Texas Instruments Incorporated

NAME

GENIQ

MAIN

SEGMENT

CODE

ISR

SEGMENT

CODE

SINTBL

SEGMENT

CODE

VAR1

SEGMENT

DATA

STACK

SEGMENT

IDATA

; Code start at address 0, jump to start

CSEG

AT

0

LJMP

start

; Execution starts at address 0 on power–up.

; Code in the timer0 interrupt vector

CSEG

AT

0BH

LJMP

timer0isr ; Jump vector for timer 0 interrupt is 000Bh

; Global variables need space allocated

RSEG

VAR1

Temp_ptr:

DS

1

rolling_ptr:

DS

1

; Interrupt service routine for timer 0 interrupts

RSEG

ISR

timer0isr:

PUSH

PSW

PUSH

ACC

CLR

INT1

; pulse LDAC low

SETB

INT1

; to latch all 4 previous values at the same time

; 1st thing done in timer isr => fixed period

CLR

T0

; set CS low

; The signal to be output on each DAC is a sine function.

; One cycle of a sine wave is held in a table @ sinevals as 32 samples of msb,

; lsb pairs (64 bytes). We have one pointer which rolls round this table,

; rolling_ptr, incrementing by 2 bytes (1 sample) on each interrupt (at the end of

; this routine).

; The DAC samples are read at an offset to this rolling pointer:

; DAC

Function

Offset from rolling_ptr

;

A

sine

0

;

B

inverse sine

32

;

C

cosine

16

;

D

inverse cosine

48

MOV

DPTR,#sinevals

; set DPTR to the start of the table of sine signal values

MOV

R7,rolling_ptr

; R7 holds the pointer into the sine table

MOV

A,R7

; get DAC A msb

MOVC

A,@A+DPTR

; msb of DAC A is in the ACC

CLR

T1

; transmit it – set FS low

MOV

SBUF,A

; send it out the serial port

INC

R7

; increment the pointer in R7

MOV

A,R7

; to get the next byte from the table

MOVC

A,@A+DPTR

; which is the lsb of this sample, now in ACC