I'm just reverse engineering a sound board...
Here's a schematic:
Who wants to have a go at explaining the address decoding and operation
Then I will compare your thoughts to my thoughts (not had a chance to test it yet, as some repairs are needed to it...)
Mark
Reverse Engineering a Sound Board...
- 1024MAK
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Reverse Engineering a Sound Board...
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
Re: Reverse Engineering a Sound Board...
okie quick look not really worked anything out.... spent more time finding out what that was hanging off the ay chip... prom uh... interesting way of adding some fixed information, set address on one of the eight bit ports, read the data in the other port...
so decoding... interesting there is no /rd or /wr but a /m1 and /iorq ... M1 must be high along with bits 0-5 on the address bus and iorq low
then looks like bit 6 is determining whether it is a read or write
and bit 7 is selecting write register select or write/read register
it looks interesting to say the least..
regards Andy
so decoding... interesting there is no /rd or /wr but a /m1 and /iorq ... M1 must be high along with bits 0-5 on the address bus and iorq low
then looks like bit 6 is determining whether it is a read or write
and bit 7 is selecting write register select or write/read register
it looks interesting to say the least..
regards Andy
what's that Smell.... smells like fresh flux and solder fumes...
- 1024MAK
- Posts: 5118
- Joined: Mon Sep 26, 2011 10:56 am
- Location: Looking forward to summer in Somerset, UK...
Re: Reverse Engineering a Sound Board...
Photo:
MarkZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
Re: Reverse Engineering a Sound Board...
Me! Me! At least the AY side of things.
The AY has 3 control pins, it's not a chip-select scheme to speak of. One of the control pins can be tied high without affecting the logic. In my case I tied BC2 high. And in this case too I see.
Here's the selection code from the ZXpand+ CPLD.
Code: Select all
// AY IO
assign AYIO1 = A[7:0] == 8'hcf | A[7:0] == 8'hdf;
assign AYIO2 = A[7:0] == 8'h0f | A[7:0] == 8'h1f;
// bdir bc1 mode
// 0 0 inactive
// 0 1 read
// 1 0 write
// 1 1 address
assign BDIR = (AYIO1 | AYIO2) & nM1 & !nIORQ & nRD;
assign BC1 = AYIO1 & nM1 & !nIORQ;
When the address port is accessed BC1 is 1.
M1 is typically factored into the logic because M1 and IORQ asserted at the same time is an interrupt ack, not an IO request.
HTH