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SOFTWARE

TLV5633C

TLV5633I

SLAS190C – MARCH 1999 – REVISED SEPTEMBER 2006

In the following example, the code generates a waveform at 20 KSPS with 32 samples stored in a table within

the program memory space of the microcontroller.

The waveform data is located in the program memory space at segment SINTBL beginning with the MSW of the

first 16-bit word (the 4 MSBs are ignored), followed by the LSW. Two bytes are required for each DAC word (the

table is not shown in the code example).

The program consists of two parts:

•

A main routine, which is executed after reset and which initializes the timer and the interrupt system of the

microcontroller.

•

An interrupt service routine, which reads a new value from the waveform table and writes it to the DAC.

;--------------------------------------------------------------------------------------

; File:

WAVE.A51

; Function:

wave generation with TLV5633

; Processors: 80C51 family (running at 12 MHz)

; Software:

ASM51 assembler, Keil BL51 code-banking linker

;(C) 1999 Texas Instruments

;--------------------------------------------------------------------------------------

;--------------------------------------------------------------------------------------

; Program function declaration

;--------------------------------------------------------------------------------------

NAME

WAVE

MAIN

SEGMENT

CODE

ISR

SEGMENT

CODE

WAVTBL

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

;--------------------------------------------------------------------------------------

; Define program variables

;--------------------------------------------------------------------------------------

RSEG VAR1

rolling_ptr: DS 1

;--------------------------------------------------------------------------------------

; Interrupt service routine for timer 0 interrupts

;--------------------------------------------------------------------------------------

RSEG ISR

TIMER0ISR:

PUSH PSW

PUSH ACC

; The signal to be output on the dac is stored in a table

; as 32 samples of msb, lsb pairs (64 bytes).

; The pointer, rolling_ptr, rolls round the table of samples

; incrementing by 2 bytes (1 sample) on each interrupt

; (at the end of this routine).

MOV

DPTR, #wavetable ; set DPTR to the start of the table

MOV

R0, #001H

; R0 selects DAC MSW

MOV

A,rolling_ptr

; ACC loaded with the pointer into the wave table

MOVC A,@A+DPTR

; get msb from the table

MOVX @R0, A

; write DAC MSW

MOV

R0, #000H

; R0 selects DAC LSW

MOV

A,rolling_ptr

; move rolling pointer back in to ACC

INC

A

; increment ACC holding the rolling pointer

MOVC A,@A+DPTR

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

MOVX @R0, A

; write DAC LSW

MOV

A,rolling_ptr

; load ACC with rolling pointer again

INC

A

; increment the ACC twice, to get next sample

INC

A

ANL

A,#003FH

; wrap back round to 0 if >64

MOV

rolling_ptr,A

; move value held in ACC back to the rolling pointer

15

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