TNDLPT : Tandy Sound on parallel port

Discussion about old sound cards, MIDI devices and sound related accessories.

TNDLPT : Tandy Sound on parallel port

Postby dreamblaster » 2018-1-09 @ 21:38

Hi,
another project in progress : TNDLPT : a parallel port soundcard that uses an SN76489AN chip.
TNDLPT.png
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Re: TNDLPT : Tandy Sound on parallel port

Postby keropi » 2018-1-09 @ 21:57

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Re: TNDLPT : Tandy Sound on parallel port

Postby SpeedySPCFan » 2018-1-09 @ 22:03

I've never owned any device capable of Tandy sound, so I'm very much interested in this. :D
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Re: TNDLPT : Tandy Sound on parallel port

Postby carlostex » 2018-1-09 @ 22:10

This was one of the concepts suggested when the lo tech Tandy card was just talk. This will only work with 386 and up, but a very welcome addition!
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Re: TNDLPT : Tandy Sound on parallel port

Postby keenmaster486 » 2018-1-09 @ 22:13

dreamblaster, will you ever stop producing the best stuff?
I flermmed the plootash just like you asked.
Very silly indeed: https://audaxeundum.wordpress.com
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Re: TNDLPT : Tandy Sound on parallel port

Postby Scali » 2018-1-09 @ 22:21

carlostex wrote:This will only work with 386 and up, but a very welcome addition!


Nope, it can be made to work on 8088 as well.
Remember that we patched various games to replace out C0h, al with int C0h? So that we could redirect them to another port on ATs, because of the second DMA controller?
For the TNDLPT we simply need to use a different TSR, which outputs to the LPT, and it can work with all patched games.
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Re: TNDLPT : Tandy Sound on parallel port

Postby gdjacobs » 2018-1-10 @ 02:38

Would you be interested in complementing it with a new Tandy 3 voice ISA card?
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Re: TNDLPT : Tandy Sound on parallel port

Postby AnacreonZA » 2018-1-10 @ 11:31

I'd also prefer an ISA card. LPT port getting pretty crowded by now.
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Re: TNDLPT : Tandy Sound on parallel port

Postby jaZz_KCS » 2018-1-10 @ 11:58

~Puts in an I/O controller card with parallel port, bringing the total number of parallel ports up to three~
Bring it on!

So this is the elusive secret project that you said would come before the OPL3LPT? I approve and are already eagerly awaiting the finished product.

Now I have to find me a nice 3d printing shop in my city to print out cases for CVX4 and OPL2LPT. As undoubtedly a certain someone will make a case for this as well one day... The anticipation rises.
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Re: TNDLPT : Tandy Sound on parallel port

Postby jaZz_KCS » 2018-1-10 @ 12:08

AnacreonZA wrote:I'd also prefer an ISA card. LPT port getting pretty crowded by now.



You have to keep in mind that these range of products seem mainly aimed at ppl with either a modern PC that still have a parallel port but ofc no ISA so they can enjoy old games with correct sound, or ppl with older laptops that lack ISA expansion slots altogether.
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Re: TNDLPT : Tandy Sound on parallel port

Postby carlostex » 2018-1-10 @ 14:35

Scali wrote:
carlostex wrote:This will only work with 386 and up, but a very welcome addition!


Nope, it can be made to work on 8088 as well.
Remember that we patched various games to replace out C0h, al with int C0h? So that we could redirect them to another port on ATs, because of the second DMA controller?
For the TNDLPT we simply need to use a different TSR, which outputs to the LPT, and it can work with all patched games.


Yes you are right. I didn't remember the int C0h patch, because i focused mainly on patching games to defeat Tandy machine detection.


All in all, i would prefer to see a multi ISA card to include, Tandy, Innovation SSI, CMS/Gameblaster and the upcoming Covox Sound Master. It would be a multi PSG card + SID chip.
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Re: TNDLPT : Tandy Sound on parallel port

Postby bjwil1991 » 2018-1-10 @ 16:46

I have the Lo-Tech Tandy Compatible Sound Card in my Packard Bell Pack-Mate 28 Plus that I purchased on eBay last year, and it sounds amazing. Too bad there isn't a Lo-Tech Tandy Sound Card that has the DAC since some games require that (Police Quest 3).
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Re: TNDLPT : Tandy Sound on parallel port

Postby Great Hierophant » 2018-1-10 @ 19:28

This is an interesting idea, but what do you intend to do with the issue that stalled the lo-tech product? That card's issue was that the sound chip's registers are not silenced on startup until written.
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Re: TNDLPT : Tandy Sound on parallel port

Postby 640K!enough » 2018-1-11 @ 03:22

AnacreonZA wrote:LPT port getting pretty crowded by now.

Well, that creates another product opportunity for dreamblaster: a multi-port "LPT bus" adaptor. Basically, a small device that plugs into the PCs parallel port and provides multiple ports, to which such devices can be connected. There are a few ways to approach such a design, but it should be quite feasible. With a unified TSR to support all of these devices, it should also be possible to make it relatively efficient.
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Re: TNDLPT : Tandy Sound on parallel port

Postby gdjacobs » 2018-1-11 @ 03:46

Great Hierophant wrote:This is an interesting idea, but what do you intend to do with the issue that stalled the lo-tech product? That card's issue was that the sound chip's registers are not silenced on startup until written.


Couldn't that be overcome with a uC and buffer logic? Latch all the required pins inactive until sound output is required? Maybe I don't understand the issue.

Maybe there's a way to have a uC performing translation between the native ISA interface for OPL2/Tandy/CMS/whatever and the requisite Serdaco parallel port device? Initialize all the requisite data structures for translation specific for the device via a DOS utility?
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Re: TNDLPT : Tandy Sound on parallel port

Postby Scali » 2018-1-11 @ 10:14

gdjacobs wrote:Couldn't that be overcome with a uC and buffer logic? Latch all the required pins inactive until sound output is required? Maybe I don't understand the issue.


The problem is two-fold:
1) A uC requires programming, so it will be more difficult for people to build their own. They not only need to solder a kit, but they also need to have the equipment to program the uC.
2) How do you determine when to mute, and when to unmute? (preferably you don't want to rely on some DOS utility, to maintain compatibility with booters, since early PCjr/Tandy games were booters).

Aside from that there's a decided anachronism and lack of elegance in using a microcontroller for such a simple 80s device.
I'd much prefer a simple discrete solution if one exists.

I personally think that just having an easy to access volume knob, or even a mute switch on the device would be good enough. Simple and cheap to build, and very effective.
Other than that, I have suggested using some kind of adder circuit, which generates the proper sequence of volume commands on-the-fly. Would probably be simpler and cheaper than a uC, and also true to simple 80s tech.
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Re: TNDLPT : Tandy Sound on parallel port

Postby AnacreonZA » 2018-1-11 @ 10:17

jaZz_KCS wrote:
AnacreonZA wrote:I'd also prefer an ISA card. LPT port getting pretty crowded by now.



You have to keep in mind that these range of products seem mainly aimed at ppl with either a modern PC that still have a parallel port but ofc no ISA so they can enjoy old games with correct sound, or ppl with older laptops that lack ISA expansion slots altogether.


Yip - I do accept that, but I would definitely be interested in buying a few ISA PCBs if they were ever produced. Sadly lo-tech's board seems permanently out of stock now and my own attempts at PCB manufacture are not precise enough to make cards like this.

I definitely prefer bare PCBs for products like this. I actually have stock of most of the necessary chips already and it's fun soldering them together in small numbers so all I really need is the PCBs themselves.
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Re: TNDLPT : Tandy Sound on parallel port

Postby matze79 » 2018-1-11 @ 12:44

Is there already some Piece of Code ? :)

Whats the Second IC ?
Clock Generatoration ?
EDIT: 74HC04
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Re: TNDLPT : Tandy Sound on parallel port

Postby Great Hierophant » 2018-1-11 @ 19:48

To shut off the chip entirely, you need to send the following four bytes to it :
9F
BF
DF
FF

I would suggest something like a 4-bit counter (with a pair of inputs unused so it functions as a 2-bit adder) that controls a line driver whose inputs are connected to +5v. When the device is powered on or a reset button is pressed, this adder does its thing and between it and the driver those logic values are sent to the chip.
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Re: TNDLPT : Tandy Sound on parallel port

Postby Scali » 2018-1-11 @ 20:48

Great Hierophant wrote:I would suggest something like a 4-bit counter (with a pair of inputs unused so it functions as a 2-bit adder) that controls a line driver whose inputs are connected to +5v. When the device is powered on or a reset button is pressed, this adder does its thing and between it and the driver those logic values are sent to the chip.


Yup, the adder can be triggered by the clock.
According to the datasheet, the SN76496 would require 32 cycles at its own clock of 3.579 MHz, which is about right (I measured that the SN76496 needs about 42 CPU cycles at 4.77 MHz for each command).
We will have a 3.579 MHz signal anyway, since that is the input for the chip itself.
So if we add a clock divider of 32 (or 64 to be on the safe side), we can use that as input for the adder (if we use a 4-bit adder and use the top 2 bits only, then we get a 'free' divider of 4x from the low 2 bits). It will make sure that the adder generates the commands at the speed the chip can handle.
Last edited by Scali on 2018-1-11 @ 20:56, edited 1 time in total.
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