Spectravideo MKI, Service – Technical Manual

Page: 80 / 134

PROGRAMMABLE
SOUND GeNERATOR
AY-3-89 10
The AY-3 -8 9 1 0
i s a r� g i s t e r o r i ent e d
p ro g r amma b l e
sou n d gene r a t o r ( PS G ) .
Commun i c a t ion be tween
t h e
p ro c� s s o r
and
t h e
PSG
i s ba s e d
on the conce p t o f
me mo r y-mappe d
1 /0 .
Co n t ro l comma n d s a r e
i s s u e d
to
t h e
PSG by
w r i t i ng to
16
me mo r y-ma p p e d reg i s t e r s . Each of the
1 6
reg i s t e r s w i t h i n the PSG i s a l s o
re a d ab l e
so t h a t t h e m i c ro proce s s or
c a n d e t e rm i n e ,
a s ne c e s s a r y , p re s e n t s t a t e s
o r s t o re d da t a va l u e � .
A l l f u nc t i ons o f the PSG a r e con t r o l l e d
t h r o u g h
i t s
1 6
reg i s t e r s wh i c h once
p ro g ramme d , gen e r a t e and s u s t a in th e
sou n d s , th u s
f re e i ng the s y s t e m p roc e s s or
for o t h e r t asks .
SOUND
GENERAT ING BLOCK
The
Bas i c
B l ocks in the PSG wh ich p roduce
t h e
p ro g ramme d soun d s i nc lu d e :
Tone Gene ra t o rs
N o i se Gene ra t or
M i xe rs
Amp l i t ud e Con t rol
Enve l ope Genera tor
0 /A
Conve r t e r s
p r oduce the
ba s ic
s qu a re wave t one f re quenc i e s for
e a ch cha nne l ( A , B , C ) .
p roduce a f re qu e n c y modu l a t e d p s e udo random pu l se
w i d th squa r e
wave
ou t p u t .
comb i ne the ou t p u t s o f the T one Gene r a t o rs and the
N o i s e G e n e r a t o r . One for each channe l ( A , B, C ) .
p rov id e s the
D / A
c o n n e c t o rs w i th e i t he r a f ix e d o r
va r i a b l e amp l i t ud e pa t t e r n . T h e f i xed amp l i t ude i s
under d i re c t C P U c o n t rol l t he va r i ab l e amp l i t ude i s
accompl i sh e d by us i ng t h e ou tput o f t h e E nve l op e
Genera t o r .
p roduces a n enve lope pa t t e r n which can be use d t o
amp l i t ude modu l a t e t he ou tput bf e ach m i x e r .
the three D/A Conve r t e r s each p roduce up to a
16
leve l ou tpu t s i g n a l as d e t e rm i ned by t he Amp l i t ude
Coot ro l .
To ou t p u t da t a f rom t h e C PU bus to a pe r iphe ra
1
dev i c e connec t e d t o
1 /0
Port
A wou ld re qu i re on ly t he f o l low ing s teps :
1 .
La tch a dd re s s R7 ( se l e c t Enab le reg is t e d
2 . W r i t e da t a t o PSO ( se t t i ng B6 of R7 to " 1 " )
3. La tch a dd re ss
R 1 6
( se l ect 20A reg i s t e r )
4 . Wr i t e dat a t o PSG ( data to be ou tput on I/0 Port A)
4 .47