9/12

PWM GENERATION WITH THE ST62 16-BIT AUTO-RELOAD TIMER

add

a,Msb_inc1

; add it to the increment Lsb

ld

Msb_ton1,a

; save the result

;*** calculation of sin(2*PI*f) with look up table ***

andi

a,03fh

; mask the Msb tone to call the look up

table

addi

a,040h

; add the result to the address table

ld

x,a

;use the indirect pointer x to read the

data

;*** calculation of the second tone ***

ld

a,Lsb_ton2

; load tone Lsb

add

a,Lsb_inc2

; add it to the increment Lsb

ld

Lsb_ton2,a

; save the result

ldi

a,0

; initiate a to 0 for no carry

jrnc

nocarry2

; test carry of the previous result

ldi

a,1

; if carry a=1 to add 1 to the Msb addition

nocarry2:

add

a,Msb_ton2

; add the carry to the tone Msb

add

a,Msb_inc2

; add it to the increment Lsb

ld

Msb_ton2,a

; save the result

;*** calculation of sin(2*PI*f) with look up table ***

andi

a,03fh

; mask the Msb tone to call the look up

table

addi

a,040h

; add the result to the address table

ld

y,a

; use the indirect pointer y to read the

data

ld

a,(y)

; read the data

;*** add the two sinus ***

add

a,(x)

; add to the first tone

;*** wait overflow ***

wait_ovf:

jrr

OVFFLG,SCR1,wait_ovf

res

OVFFLG,SCR1

; reset the overflow

;*** load compare register with a new value ***

ld

CMPL,a

jp

DTMF

;*************Subroutine Tone Generation **************

;*** Input with accumulator a for the number to make

InitTone:

ldi

drwr,21h

; Rom window with num_dial

sla

a

sla

a

addi

a,40h

ld

x,a

ld

a,(x)

ld

Msb_inc1,a; First tone