MECB 6809 Testing, Coding, Sound!

[Editor]

Couldn't help myself - I wrote a really basic VRAM memory checker (working through filling with zeros, filling with FFs, filling with AAs, filling with 55s ...

Awesome work! I did a similar VDP memory test, but instead via an Arduino sketch, as part of the development and verification of my "Alternate VRAM Solution" (which then formed the basis for the MECB TMS992x VDP Card VRAM design).

You can find this code here: https://github.com/DigicoolThings/TMS99 ... x_VDP_Test

At the time, I briefly thought this might also make a good candidate for making a simple "realistic circuit use" 4464 DRAM chip tester. But, then I remembered we are only actually using the first 16Kx4 of the 4464 64Kx4 DRAM's. So, it would be an incomplete DRAM chip test. LOL.

I didn't bother to migrate the VRAM test across into 6809 code, as I was, by then, happy that my VDP 4464 memory interface design was solid.

If you're happy to share your test code, you could either post a link to your repository here, or alternatively, I could add it to the MECB github repository (assuming you're happy to do this and have added a suitable header that assigns credit to yourself as the author).

For sound testing, remember the 6809 Christmas Demo, which tests the VDP, VDP Frame Interrupts, and also SN76489 Sound (on the Motorola I/O Card), here: https://github.com/DigicoolThings/MECB/ ... tmas09/src

[epaell]

Sure, once I get my act together I'd be happy to add the test code somewhere. LOL, it re-uses <cough>pilfers</cough> a lot of the code you had already written for the VDP but slightly modified for this particular check and ties it in with the ASSIST09 routines so that I can write the progress and results to the terminal. I'll see how I go this weekend but will definitely try the Christmas Demo (that's what I was running previously but got concerned when no video was coming out and so didn't even think about checking the sound side of things more carefully at the time).

[Editor]

Sure, once I get my act together I'd be happy to add the test code somewhere. LOL, it re-uses <cough>pilfers</cough> a lot of the code you had already written for the VDP but slightly modified for this particular check...

LOL. Well, the best way to write new code, is to leverage code that has already been written. Avoid re-inventing wheels, if the function has already been implemented satisfactorily. Well, that's what I say.

[epaell]

I'm definitely a fan of not re-inventing wheels!

I had a quick try again this morning before starting work and confirmed there is no audio. While looking more closely at the board I noticed that the SN76489 I ordered had solder shorting pins 1 and 2. I removed that but it still didn't work ... then realised I bent pin 8 when re-inserting it into the socket ... fixed that, but still no go - sigh! There is activity on the data bus, the clocks are all there but just not much happening on the SN76489 itself (or the PIA output). I'm suspecting either a problem with the PIA or the SN76489 - but given that I can't see if the video is really working (with the Christmas Demo) it is a bit hard to tell e.g. if it's not getting IRQs then that would prevent the PIA/SN76489 from being updated. I may need to go back to basics and check that if I write things out to the PIA port that they are actually reflected in the port pins and just manually send the codes to the SN76489 to see if I can get it to do something (or just write up a simple test program ... though I'd probably need to pilfer some more of your code from the Christmas Demo as it's been decades since I lasted worked with a PIA.

[Editor]

I may need to go back to basics and check that if I write things out to the PIA port that they are actually reflected in the port pins and just manually send the codes to the SN76489 to see if I can get it to do something (or just write up a simple test program ...

Sounds like a plan. You mentioned earlier that you had an oscilliscope, so it sounds like you have all the tools / skills necessary to trace the problem.

From your description, it does sound like the condition of your SN76489 makes it a prime suspect. I wouldn't think that shorting pins 1 & 2 (D1 & D2), would've caused any permanent damage to the PIA port (or the SN76489). Also I see pin 8 is the GND power pin.

Given also that you've already checked the basics like clock is present (pin 14), and activity on the port / data pins (and also PIA CB1/CB2 ??), when the Christmas Demo is running, further makes me think the SN76489 might be suspect if no sound output is present (pin 7).

But, fault diagnosis is always part of the fun, and satisfying to resolve!

[epaell]

I can pretty much confirm that the sound chip is not well (it's dead Jim!).

I modified the Christmas Demo so that it just tests the sound chip (removing all the interrupt and VDP-related items so it is as simple as possible and included what was originally in the interrupt handler into a loop). I also added some console outputs to let me know where in the code it is at any point. When running, it immediately gets stuck in the writeSoundByte function when trying to silence the audio (waiting for the chip to signal that it is ready). I checked the ready pin and it is always high. I tested if this was the problem by pulling out the chip and then manually grounding the ready pin and that allowed the code to progress. So I think that indicates that the PIA is working at least.

Ah well, I ordered some more audio chips from another provider ... but have to wait again for them to arrive

[Editor]

Ah well, I ordered some more audio chips from another provider ... but have to wait again for them to arrive

If it's any consolation, I have varying luck with sourcing retro recovered chips. Well, you've seen my videos on falsly re-marked chips.

Even with the likes of EPROMs, I often get several failures in an ordered batch.

What I've learned is that if you need one IC, you're best to order at least three! I usually order chips in 5 or 10 quantities.

Although, my last delivery (of 5x TMS9918A chips) was actually a sealed empty bubble envelope. The first time I've been fully scammed.
I got my money back (AliExpress are pretty good at that). But, it does add another month delay to that project, while I await another order of 5 chips (from a different seller). I only need one working one!

[epaell]

I'd have to admit that I've actually been pleasantly surprised (for the most part) with what I've received so far from Aliexpress (although sometimes the packing seems very minimal e.g. a small plastic seal-lock back inside an envelope). LOL, receiving an empty bubble envelope is bizarre (and frustrating) - I think the loss in time is what I'd find most frustrating. Hope your next order turns out OK.

[epaell]

Woohoo! Video converter just arrived in the mail ... and can confirm it is a Good Friday ... the video card was working after all (just ran the Christmas Demo and that works, well, without the sound because I'm still waiting for a replacement sound chip)

I'd post an image of the working system but I'm not sure how to do it.

[Editor]

Woohoo! Video converter just arrived in the mail ... and can confirm it is a Good Friday ... the video card was working after all ...

That's awesome to hear! Please give us all the details.. see image link example below.

I'd post an image of the working system but I'm not sure how to do it.

To post an in-line image you need to use an image hosting service that supports SSL secured links (https).
For example imgbly.com (free image hosting).

An example of the format your image link should look like (in editing your comment), is below.
This is an imgbly hosted raw image https link:

Code: Select all

[img]https://www.imgbly.com/ib/PPqjuUXrGe.jpg[/img]