FPGA replacment for the ZX8301 ULA and more

[lliont]

Hi Leon,

long time no talk. Hope you are doing well? I have a more basic question,. Do you plan to make your development available to the community as a ready plug in board. Maybe to different version:

1. Just a basic ZX8301 replacement. No extras just the most simple one?

2. The most sophisticated version, with all the ad ons?

Stephan

Hi Stephan

The basic cpld version is already available to the community with and without any extras at hackaday.io, look at the files section for the older_ula.zip with description "Files of the older more compact ula board without the AD724 IC" . There you'll also find of course the version with the color mixer and pal encoder.
https://hackaday.io/project/187455-zx83 ... inclair-ql

The most sophisticated fpga pcb is not finalized yet but this is going also to come in versions.
One with 7.5Mhz CPU (but faster than the standard) with 2MB ram, colors, qlsd, sprites etc that will be compatible with many external cards like floppy controllers etc.
And one or two versions with faster cpu clock that makes the external cards incompatible (also mostly not needed).

The need of a simple basic ULA replacement is covered, this is the one:

Just build it, program it and plug it in the socket, no connections needed but if one wishes it has a 16 color mode that can be enabled.

[martyn_hill]

Even better I may add a counter with programmable frequency divider.

Now that would be cool! (I say 'cool', but I mean of real value...)

[Peter]

Just build it, program it [...]

I don't think that is what Stephan meant with "a ready plug in board"...
Curious myself, as I would buy one - especially if it was more compact - but not build one.

[lliont]

I see, I will make the basic cpld board more compact and then build some (basic cpld ula replacements).
So when someone is interested he can send me a message, I haven't received much requests so I wasn't aware if there is enough interest.
When I'll make the more compact pcb I'll make a new topic.

[Pr0f]

I think there is a good deal of interest in a direct or enhanced but basically compatible ZX8301.

Enhanced could mean:

output to VGA rather than composite signals
Better protection of Video output signals (as this is the main failing of the ZX8301 in QL's)
Faster memory access times or reduced waiting on video accesses
change of colour palette

[Peter]

I see, I will make the basic cpld board more compact and then build some (basic cpld ula replacements).

That's very good news! I will buy at least one. Many thanks.

So when someone is interested he can send me a message, I haven't received much requests so I wasn't aware if there is enough interest.

I think this is the big difference between software and hardware development.
An open source release makes software available, but not hardware...
I would estimate that 80% of the potential users can not solder your board or have difficulties sourcing the components.
And half of the remaining 20% - including myself - are too busy with other stuff.

The ZX8301 is the most wanted QL chip and has the tendency to break.
I'd estimate you can sell at least 20 boards within a few months.

[Peter]

Better protection of Video output signals (as this is the main failing of the ZX8301 in QL's)

I think this is already ensured by Leon's design.

Faster memory access times or reduced waiting on video accesses

Personally I have a different taste here. If I replace the ZX8301, I want exactly the same timing behaviour.
I'd like to be able to use my original QL 100% retro, be it for test purposes or ancient software.

[Pr0f]

I'd be interested to know how much of the 'ancient' software would actually have issues with video / memory timing changes. The Vsynch interrupt which seems to be used by the job scheduler as it's main default tick (although - before you all jump down my throat here - I know that it can cycle around the loops more frequently when it can) - but I suppose some games may be making precise timings on the CPU / Video frame timings.

I suspect the QEPIII has some timing dependencies as well and makes use of the 'E' signal from the CPU.

[Andrew]

I see, I will make the basic cpld board more compact and then build some (basic cpld ula replacements).
So when someone is interested he can send me a message, I haven't received much requests so I wasn't aware if there is enough interest.

I am interested in a basic ula replacement that can use 16 colors and, if possible, change of colour palette.
I am not a hardware person, so building one myself is out of the question

[xelalex]

I would be interested in a basic ULA replacement as well. Still have a QL mainboard with dead ULA that I could get back to life with it.