CPLD replacement for ZX8301

[Pr0f]

How big a footprint is the solution in terms of macrocells ?

[lliont]

all the 160 macrocells (of the EPM7160S)

It easily fits in Xilinx XC95288XL-10-TQ144 3.3V and 5V tolerant, but this is almost equally obsolete, isn't it;

[Peter]

Hi Peter, because it works and I'm lazy

You are not lazy, and to save work is of course a valid reason. I just wanted to understand.

Make a suggestion of a new 5V tolerant and of the same size/price cpld and I'll try it.

If you had not already filled all 160 macrocells, I'd have suggested the Lattice LC4128. Unfortunately, the next size step within that family is 256 macrocells, which would be twice as expensive as your Chinese supplier. The ECP5 series FPGA which I use for the Qzero has recently been complemented by a non-BGA cased variant. It is not directly 5V tolerant, but has internal clamp diodes, which I use in combination with series resistors for 5V tolerance. The advantage would be that 64 KB SRAM are on chip, even on the cheapest, smallest size. And endless resources to play with palettes etc. Disadvantage: You'd need 3 supply voltages, a serial config flash, and the learning time for modern FPGA.

I don't know if the 3.3V outputs can drive the noisy QL circuit correctly although I believe they are TTL compatible and will most probable do.

That is no problem, but the fast slewrate of newer devices could be. I was wondering if you were using obsolete chips for that reason.

Currently EPM7160S are available from ebay sellers, 10€.

I know, but only Chinese, which means risk to spend hours for a visit to customs office. And higher risk of sick chips than buying in Europe.

[lliont]

Hi Peter, thanks for the suggestions.

and the learning time for modern FPGA.

No learning time needed see this: https://hackaday.io/project/162876-lion ... pucomputer
I used Cyclone V 5CEFA2F23I7 and I used the method with the internal clamp diodes in combination with series resistors with success in this project to interface with PS/2 keyboard.

There is extra complexity for the support circuit of a fpga and bigger cost, it would worth it If there was more to achieve.
It would worth it for sure if I was to add sprites and vga output as I have already mentioned in a previous post.

I never had problem with customs here for small quantities, the only problem is the long delay.

Also I have already compiled the code for the Xilinx XC95288XL which is a newer and bigger cpld with the same cost from ebay/China and I have almost finished a pcb for it.
So there is an alternative already.

[Peter]

No learning time needed see this: https://hackaday.io/project/162876-lion ... pucomputer

Very impressive. The Java Grinder idea is amazing, I noticed there are even 68K targets. I only wish you had done that for the QL

There is extra complexity for the support circuit of a fpga and bigger cost, it would worth it If there was more to achieve.

That is why I mentioned Lattice ECP5. Practically I get below PLD prices with 12K LUT. About 6.50 € before the chip crisis, and 9.50 € afterwards. I use a dual LDO for 3.3V and 2.5V, in SO8 package to get decent current. And a separate small one for the core voltage. With some tricks, I can manually solder BGA for prototyping. Once I had figured it out, it felt less work for me than TQFP. (I wouldn't hand solder both for a series.)

I never had problem with customs here for small quantities, the only problem is the long delay.

Not a problem as such, but I have a long drive to the customs office, must wait there, and drive back. Everything that is not officially shipped DDP and worth more than 5.26 € can nowadadys end up there.

Also I have already compiled the code for the Xilinx XC95288XL which is a newer and bigger cpld with the same cost from ebay/China and I have almost finished a pcb for it.

A 50 € chip, if bought from authorized distributors, but glad to see it is not obsolete yet. This gives some safety, should a ULA replacement become a necessity someday. I just have no explanation why it can cost five times less in China without a catch to it...

[lliont]

I finally managed to test the pcb with issue 6 and 7 motherboards and it works well.

[Maskenlos]

Hi Leon,

really great achievement with your newest upgrade. I have a question about project documentation. Do you plan to share the details for the lastest development step also on your hompage? Also May I make a suggestion? As there have been some evolution steps, do you plan to summarise these steps incl documentation on your project page? Means for example:

a) Basic ULA replacement just with CPLD and buffer chip and probably scart out. Sub versions with different colour option like orange maybe
b) Same as a) but with additional PAL video encoder
c) Latest state with Video RAM

All this linked to the schematics, Gerber, CPLD code whatever you are willing to share.

I guess this would be helpful to many forum members to build their on unit.

Thanks again for your great effort and your support.

Stephan

[lliont]

Hi Stephan

The last upgrade is very nice, you can see the difference in a simple dir or list command, QL scrolls faster and also games are faster.

I'll make a summary when I finish with the new pcb I am waiting, for the Xilinx cpld but I haven't decided if I'll make public the fast lower/video ram version.

[Maskenlos]

Hi Leon,

I haven't decided if I'll make public the fast lower/video ram version.

Fully understand. It is totally up to you and I really appreciate what you already shared to the community and your very friendly and helpful behaviour!!

I am just thinking if a QL fellow is seeking for an ULA replacement and come across this discussion. May be you could consider to make a zip file, a bundle with the information to build a ULA replacement without any additional functionality. Just a 1:1 replacement with the original ULA. This may contain the Gerber, The CLD code, schematics and just 2-3 links where to get the oscillator and the CPLD and maybe 1-2 picture. Means one of the early but stable version you had on your project page but is gone due to further development. And then share in this Thread

Just my thoughts.

Thanks,

Stephan

[XorA]

Looks like all this project needs now is Aurora mode implemented to have an Aurora workalike in combination with an SGC