TLV5614

2.7-V TO 5.5-V 12-BIT 3-

µS QUADRUPLE DIGITAL-TO-ANALOG CONVERTERS

WITH POWER DOWN

SLAS188 – 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 Inc.

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

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 cosine48

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