Another ATARI 7800 New Cartridge PCB with SN76489 and YM2413 Simultaneous Support

[+selgus]

While designing and building a new ATARI 7800 cartridge pcb that supported the POKEY and a YM2413, though not at the same time, other developers were talking about being able to use multiple sound chips on the 7800, simultaneously.

 

I did a design with the POKEY and YM2413 that could be used at the same time, though it's not really practical or worth it. So I moved away from the POKEY and turned towards the TI SN76489. They are readily available, cheap and from some of the vgm music I've heard with the sound chip, it seems like a good direction.

 

So I started development on this new pcb. I'm pretty far into this version, with the pcb schematic finished and board layout. I needed to move to the atf1500a cpld, instead of the gal I was using on previous versions, as I needed more i/o pins for the functionality and logic. That the point I'm at now, designing the logic that runs on the cpld..

 

[+selgus]

Worked on this pcb a bit more. I want to thank @Eagle and @rj1307 for sharing information and support from their implementation of the SN76489 on their flash cartridge. I needed to add support for locking the data lines while writing to the SN. I tried to get this logic into the cpld, but I didn't have enough i/o pins to create the flip-flop, so I added a flip-flop to the pcb, driven by the cpld. I needed to move things around and re-layout parts of the pcb, but that is completed now.

 

[Eagle]

MatGuru found 2413 core

I bet that he will put in SN² cart by tomorrow  

 

https://github.com/MiSTer-devel/SMS_MiSTer/tree/master/rtl/VM2413

[+saxmeister]

The SN 76489 is a great option as a viable sound chip to add to these carts. The classic home systems, computers, and arcade machines (Mr. Do, Mr. Do's Wild Ride, Wonder Boy: Monster's Lair, and so on...) have such great music that could be emulated on the 7800.

 

Don't get me wrong: I love the POKEY/HOKEY, and I love the Yamaha FM chips, but the SN 76489 has a neat character that fits the time period and is probably the closest to the AY-3-8910 chip (which is another I'd love to have-think about how easily we could recreate the Discs of Tron music with a pair of these on a cart!) in character and capabilities.

 

Comparison of SN76489 and AY-3-8910: 

 

 

[+selgus]

I took one more revision of this pcb, this time changing the cpld to the atf1504as, which has around 3x i/o pins. This now allows me to remove a few ics, the inverter and flip-flop now being implemented in the logic. I also now have all the data lines as input and can handle 8K rom banks, instead of 16K ones.

 

[+batari]

On 2/17/2024 at 7:16 PM, saxmeister said:

Don't get me wrong: I love the POKEY/HOKEY, and I love the Yamaha FM chips, but the SN 76489 has a neat character that fits the time period and is probably the closest to the AY-3-8910 chip (which is another I'd love to have-think about how easily we could recreate the Discs of Tron music with a pair of these on a cart!) in character and capabilities.

I should point out that HOKEY is not just a POKEY replacement. While there is a point about using actual legacy sound chips - that is cool in its on regard - HOKEY should eventually be able to replicate the POKEY, the SN chip and Yamaha FM chips.

[+selgus]

Okay, really my last revision of this pcb! 😀

 

I made the via pads on my jtag connector too big for the pogo pins I wish to use for programming (I don't want to have an actual jtag connector on the board, that would be used just once). So while adjusting that, I decided since I already modified the board to support 8K banks, instead of 16K ones.. I have extra i/o pins, let me add support for 4K banks. This allowed me to clean up some traces too, so win-win.

 

[+karri]

1 hour ago, selgus said:

I have extra i/o pins, let me add support for 4K banks

This is really a good decision. The holeyram banks are 4k. I was a bit confused by the plan to use 8k banks.

[+selgus]

I found a pre-made cable with built-in pogo pins, plus registration pins, so I did make a slight change to my pcb. I made a footprint for said cable connector and reworked that area to make it fit. I'm going to make some test boards for this one instead of the previous design.

 

[Eagle]

Let me know if you need some test programs for banking or music. 
 

[+saxmeister]

@Eagle you are an incredible resource here at AtariAge and I personally want to thank you for reaching out and adding so much to this community. Always helpful and knowledgeable. Because of you I'm finally going to be able to code some of the games that I wanted to do before. And here you are helping again.

 

@selgus I want to say the same to you for your dedication and contribution to the entire scene. These cart PCBs are so great!

[+selgus]

Got my boards today, will build one up after I finish assembling the 7800 Portable pcb first (since it is currently on the workbench electronics table)..

 

[john_q_atari]

2 hours ago, selgus said:

Got my boards today, will build one up after I finish assembling the 7800 Portable pcb first (since it is currently on the workbench electronics table)..

 

It's a beautiful looking board. 😍

Edited February 29 by john_q_atari

[+selgus]

Assembled one up.. still need to deal with the cpld programming. Pay no attention to the 18-pin socket being used for a 16-pin ic. I couldn't find an ultra-low profile machine socket in 16-pin configuration at my normal suppliers, so I just popped out the two top pins and magic.. 16-pin version.

 

 

[Obiwan]

Hi Selgus! I have been following you and this thread for months.

 

Though I have no knowledge in circuit conception, I'd like to understand how you did it. Why did you put some resistance or capacitor? What is the purpose of each component? And what books I should read to acquire these fundamentals?

[CPUWIZ]

18 minutes ago, Obiwan said:

Hi Selgus! I have been following you and this thread for months.

 

Though I have no knowledge in circuit conception, I'd like to understand how you did it. Why did you put some resistance or capacitor? What is the purpose of each component? And what books I should read to acquire these fundamentals?

 

Get the book "The Art Of Electronics".

[Maztr_0n]

On 2/23/2024 at 12:12 AM, batari said:

I should point out that HOKEY is not just a POKEY replacement. While there is a point about using actual legacy sound chips - that is cool in its on regard - HOKEY should eventually be able to replicate the POKEY, the SN chip and Yamaha FM chips.

Seems like the future!

 

Hope its used in many games soon.

 

But also either way thats just cool.

[Obiwan]

On 8/17/2024 at 11:04 AM, CPUWIZ said:

 

Get the book "The Art Of Electronics".

Thanks you!

[Clint Thompson]

Looks great!

 

Would love to see/hear a video of this running something using the sound chip! 

[Eagle]

5 hours ago, Clint Thompson said:

Looks great!

 

Would love to see/hear a video of this running something using the sound chip! 

 

 

[Clint Thompson]

Super rad to hear, thanks!