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Tandy Sound Compatible PCB

The simple pull down until first read was always the intention. Development of this is likely to restart next week.
 
I wonder if we could use a 74HC93 for my earlier idea of using a counter to generate the volume commands.
It has a 'master reset' which we could connect to the ISA line I suppose. This will force the counter to 0 whenever the system is reset.
Then you can let it count up with an edge-triggered signal.
It has a 4-bit output, which we could use to generate the two bits we want, and a 'carry'.
We can use the inverted carry to generate the 'fixed' bits in the 1xx11111 pattern we are looking for. That would turn them into 0xx00000 once we counted to 100.
xx will be taken from the first 2 bits of the counter output directly.
That part would take care of the actual commands.

When there is no 'carry', we are in 'init' mode, so we block the ISA bus (with some and ports?).
Once the 'carry' goes high, the circuit outputs 00000000, and we just want to ignore it, and unblock the ISA bus.

Then what we would still need, is to do the actual handshaking with the SN76489 to process the data, then pulse the counter to increment by one, and process the next data.
I don't understand the exact communication between the SN76489 and the ISA bus... but I suppose it is something along the lines of us having to signal that we want to write to the chip... the chip then signals that we can (which we can ignore I suppose), and it will take the data from the 8 input pins, and then signal ready?
In which case, could we 'hardwire' the write signal with the inverted carry, and use the ready signal to pulse the counter?

Probably needs some finetuning, but... is there any merit to this idea?
It'd be clean and simple, and wouldn't require any programming of ROMs or such.
 
Why so complicated ? just use a other Amp with Mute Function. Or add mute circuit to lm386.
(As far as i remember putting Pin 7 on GND mutes LM386)
use a latch on the ISA Bus and on boot call a small asm program who disables mute.
 
I have a v1 board working well in an IBM XT now. The PC speaker input picks up some RF noise but nothing too bad.
The omission of an external volume control isn't an issue really either, as can always plug in headphones or a speaker with volume control.
This machine has an XT-IDE so I modified the bios to also set the volume to zero, this happens right after memory check (20 seconds or so after power on)

Overall it's a nice simple design and the shortcomings aren't a big deal IMO.
 
Indeed, the v1 board works well enough for me.
I'd be happy with a v2 board that simply:
1) Fixes the design flaws in the PCB, so we no longer need to use patch wires to assemble them.
2) Places the volume controls on the backplate of the card, so they can be accessed from the outside.
 
DSC_0070.jpgphoto_2018-07-14_14-17-10.jpg

i have now a working tandy isa board, which mutes amp on boot and on system reset.

there still few things todo,

- write a TSR for supporting newer Machines, port remap.
- write a proper muting utility for silencing all channels after boot
- proper documentation
- better firmware for attiny13 :)

Prototype:
prototype.jpg
 
View attachment 46734View attachment 46735

i have now a working tandy isa board, which mutes amp on boot and on system reset.

there still few things todo,

- write a TSR for supporting newer Machines, port remap.
- write a proper muting utility for silencing all channels after boot
- proper documentation
- better firmware for attiny13 :)

Prototype:
View attachment 46736

Excited to see this finally take final form. More than happy to test some prototypes, how'd you work the mute circuit out?
 
Excited to see this finally take final form. More than happy to test some prototypes, how'd you work the mute circuit out?

The ATTIny controls the transistor which mutes the LM386 using its bypass pin.
its pretty simple,

ATTiny is waiting few ms until bios has done port access, after that it waits for CE, if CE signal is enabled it enables the LM386.

Muting Tool is still required to be sure every channel is set to the same value.

Still have some Fun with System reset.

hopefully you can understand my writings as english is not my native language :)
 
System Reset now works also, but on Soft Reset, its not muting again.

Resetbutton is fine, here i can use isa reset signal.
 
Now we got a Port intercepting TSR.

https://github.com/pdewacht/lotech

only supporting QEMM!, EMM386 is unsupported.

Allows running Card on 2C0h and play Tandy Games/PcJr/PS1 Games without patching them.
Disadvantage, 386 needed.

allows usage of the Card on machines that can't use 0C0,
 
This is already based on this code, pdw is developing the adlipt code and also this code.

But emm386 will never be able to work with tandy ports, it simple can't intercept 0C0h.

i will upload Schematic and Firmware to add silencing mcu to existing lotech cards :)
 
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