Texas Instruments TMS370 Series, Application Book

Page: 112 / 565

93
; SINE WAVE UPDATE LOOP – 179 MACHINE CYCLES = 100
µ
S
;
; ADJ ADDED TO PREVIOUS ADJUSTMENT TO SINE TABLE
; CNT ADDED W CARRY TO PREVIOUS LSB OF 16 BIT SINE TABLE
; MSB OF 16 BIT ADDR FIXED
;
; REPEAT FOR EACH DTMF DIGIT
;
; DTMF: ADD SINE VALUES AT BOTH ADDRESSES
; SHIFT RIGHT (NORMALIZE)
; OUTPUT TO LOW NIBBLE OF BPORT
;
LOOP
.EQU $
;
; DTMF FREQUENCY 1
MACHINE CYCLES
; ––––––––––––––
ADD ADJ1,PRT1+2 ; ADD ADJUSTMENT 9
ADC CNT1,PRT1+1 ; ADD COUNT 9
AND #03Fh,PRT1+1 ; 6-BIT ADDRESS 8
MOV *PRT1+1,A ; 9
MOV A,B ; 9
;
; DTMF FREQUENCY 2
;
ADD ADJ2,PRT2+2 ; ADD ADJUSTMENT 9
ADC CNT2,PRT2+1 ; ADD COUNT 9
AND #03Fh,PRT2+1 ; 6-BIT ADDRESS 8
MOV *PRT2+1,A ; 9
ADD B,A ; SUM INDECIES 8
RRC A ; NORMALIZE 8
;
TST B ; DELAY 10
TST B ; FOR LOOP 10
TST B ; = 179 10
INV B ; MACHINE CYCLES 8
;
MOV BPORT,B ; 7
AND #0F0h,B ; 6
OR A,B ; 7
MOV B,BPORT ; 8
;
INCW #–1,TIMER+1 ; 11
JC LOOP ; 7 (JMP TAKEN)
; –––––––
; TOTAL 179
;
SETMID .EQU
$
MOV BPORT,B ; SET OUTPUT
AND #0F0h,B
OR #008h,B ; TO D/A MIDPOINT
MOV B,BPORT
RTS
;
;***************************************************************************
;
DIGIT
.EQU $ ; DTMF DIGITS
;
; DATA LX,HY LX = LO FREQ TABLE INCREMENT
;
HY = HI FREQ TABLE INCREMENT
;
.WORD L4,H2
.WORD L1,H1
.WORD L1,H2
*