PICO9918: A drop-in replacement for a TMS9918A (with source)

[J64C]

I wrote a small exe utility that puts the Pico in to upload mode automatically and have it run after a compile, and uploads the new UF2 at compile time.

Was one of the best things I ever did. Saves so much time and fiddling. You don’t have to touch the Pico again.

When I’m in front of my PC next I’ll see if I can upload it somewhere, if anyone is interested.

[barnacle]

Sadly, exe files are studiously ignored by my linux toolchain but never mind.

Though I have managed to advance from blinky to a vga demo on a couple of different toolchains - raw CLI and an arduino variant. Hopefully I shall have time today to see if its actually outputting anything useful... in which case I can proceed to make it do what I need.

At the moment its about as enigmatic as a certain black monolith in 2001...

Neil

[Yuri]

barnacle wrote:

At the moment its about as enigmatic as a certain black monolith in 2001...

I can't let you run that non-ELF binary Dave.....

[barnacle]

Well, I have video coming out though there are a lot of issues with the demo that I got running, not least that it uses a double scan (640x240) screen to provide double buffering; not something I need.

I'll make further comments, when I have some, on a separate thread as I seem to have derailed this one

Neil

[visrealm]

I have just released the Gerbers for the PICO9918 PCB v0.3. I've been running tests continuously for a week or so on this revision and it is working great. 

I've been thinking about how to go about getting this tested on more machines as I've only tested on two TI-99/4A's (PAL and NTSC) and my HBC-56. I might produce a few of these to send out to those who are willing and able to try it on a wider range of machines. Let me know if you're interested in this.

Note: This PCB revision is not representative of the final release which will be a single board without the need to the piggy-backed Pi Pico board. However, v0.3 is fully functional. If you're a tinkerer or early-adopter type, go ahead and give it a go. If not, I suggest waiting.

https://github.com/visrealm/pico9918

[cbmeeks]

visrealm wrote:

I have just released the Gerbers for the PICO9918 PCB v0.3. I've been running tests continuously for a week or so on this revision and it is working great. 

I've been thinking about how to go about getting this tested on more machines as I've only tested on two TI-99/4A's (PAL and NTSC) and my HBC-56. I might produce a few of these to send out to those who are willing and able to try it on a wider range of machines. Let me know if you're interested in this.

Note: This PCB revision is not representative of the final release which will be a single board without the need to the piggy-backed Pi Pico board. However, v0.3 is fully functional. If you're a tinkerer or early-adopter type, go ahead and give it a go. If not, I suggest waiting.

https://github.com/visrealm/pico9918

I have many machines that I could test on. I also have three Pico clones you mentioned on your repo in addition to about 8 normal Picos. I more than likely have all the parts I need to build a board (except the board).

As for vintage equipment to test, I have around 8 or 9 TI-99/4a's, two ColecoVisions and a Coleco ADAM.
I would love to help out.

[visrealm]

cbmeeks wrote:

I have many machines that I could test on. I also have three Pico clones you mentioned on your repo in addition to about 8 normal Picos. I more than likely have all the parts I need to build a board (except the board).

As for vintage equipment to test, I have around 8 or 9 TI-99/4a's, two ColecoVisions and a Coleco ADAM.
I would love to help out.

Perfect!

If you're willing to order the PCBs directly from JLC, it will likely be cheaper than I could send you one from Australia:

Otherwise, I could build one up and send to you.

[visrealm]

Started working on the next revision of the board (v0.4). The all-in-one.



Looking pretty good. Managed to have it mostly single-sided (good for cheaper PCBA). Most of the components will be on the underside. 4 layers with the middle layers being a solid ground pour and a (mostly) power layer. Signals mostly on the IC layer (bottom) with some on the back (top).

On the top side are a couple of optional LEDs for read and write (for those who like the blinkenlights). The Boot button and USB-C connector required for reprogramming to little RP2040.

Not ordering these yet as I like to give it a few days to "simmer" in case I think of anything I've missed or could do better. Likely order the initial batch next week.

[cbmeeks]

I didn't realize you were all the way down there.

I will see about ordering some PCB's.

[cbmeeks]

PCB's ordered. It's going to be a while because I got the slow-boat shipping. And, I just realized I don't have some of the SMD parts.

[visrealm]

Nice one. I (almost) always get the slow-boat shipping. It's still reasonably quick for the price.

I still don't understand the pricing. I can get boards manufactured and shipped here for less than I can send a similarly sized package within Australia.

[cbmeeks]

It has something to do with the "last mile". For example, China (somehow) sends the item for next to nothing to the US shore. Then, our postal service (USPS) provides the shipping to our house. Which I'm sure the USPS does not like because the shipping I had to pay was less than $2.00 USD.

[barnacle]

In Europe, the tax laws changed last year so that incoming small packages are now taxed, which has increased the cost slightly, but at least there are no issues with customs since its all included in the price (as is e.g. Mouser and Digikey which in spite of Eurozone offices, supply from the States).

Farnell supplies from inside the zone, but is generally pretty expensive as a supplier - and like the other big suppliers, has a minimum order fifty or sixty bucks - for free delivery. Other German suppliers tend to lack the range of the big three, and are generally pricier to boot.

I find LCSC handy _if_ they've got stock. Usually they have, but sometimes I'll find a dozen parts all with zero stock. But they're usually the cheapest supplier around, and if I have to wait for JLC to deliver the board, I may as well wait for LCSC to deliver the parts. Or get JLC to make the board using LCSC parts, though I've not tried that yet.

Neil

[visrealm]

Still waiting on parts to assemble, but the v0.4 PCBs have arrived and look great. Seen here next to their prototype predecessor and an original TMS9918A.

Given this is my first PCB designed to take an RP2040 directly, I wouldn't be surprised if there are issues, but hoping for a usable board. I should have the parts to build one early next week.

[cbmeeks]

I just got my v3 boards. I will be ordering the SMD parts to finish them very soon then I will start testing in some TI's.

Also, a friend of mine has a Coleco ADAM with no video. I hope to try it in there too.

Next, I have my own Coleco ADAM and two ColecoVisions. On of which has fried DRAM which this should actually fix.

More to come!