CPLD replacement for ZX8301

[Pr0f]

viewtopic.php?p=24729#p24729

[bwinkel67]

those chips are a world apart.

The inteface 1 ULA did not do much in other than offer some connection ports - the actual 'control' of the network ports, serial port was all done with software in the ROM in the Interface 1, I don't think much more assistance was provided to the Microdrive interface either.

The ZX8302 does have some registers, and devices built in that do a bit more than with the data before the QL's micro needs to get involved - perhaps with the exception of the QL network ports - which I think were still bit banged in the end.

From memory:

2 interleaved shift registers for data reception and transmission for Microdrive data
Microdrive motor selection logic
Microdrive Write inhibit (not implemented in the end on the chip)
4 byte binary counter with battery backed capability for the QL clock (battery backup never worked as resetting the computer often corrupted the counter)
Serial transmission shift register (the IPC handled serial reception)
Bit banged interfaced for the QL network
Bit banged interface for the IPC (that handles keyboard and sound)

I believe there is a thread on here by Nasta about the ZX8302

Ah, so you'd have to update the ROM to do more and then of course the chip communicating with the QL would be a whole different beast. I do recall having a conversation with Charlie on how the ULA did most of the microdrive communication work. I'm assuming that part is shared though between the two chips. I was just wondering if that ULA (and ROM) could be used as a springboard to develop a ZX8302 replacement, or if it would just be easier to start from scratch.

[lliont]

I present to you the new Leon ULA clone with 64K static ram shadow of the video ram.
It increases the performance of QL about 30% for programs run at the lower 128K or any program that access the video ram.

I received the pcb today and just assembled it and debugged it. I run the simple test program that prints 500 numbers that in the stock QL takes about 51 secs but with this ula it took 37.4 secs
Fast mode is the default but can enter normal mode again with poke 98401,64
I kept the 16 colors but choice of palette for the 16 colors doesn't fit so no orange in this one maybe in the future.
I'll do more tests and development to see if I can do better.

[Derek_Stewart]

Hi,

Looks great, looks another QL addon I want.

[Maskenlos]

Hi Leon,

great next step! Thanks for sharing here. It is really fun to play around with your development.

Stephan

[Cristian]

Great progress!!

[Pr0f]

Any plans to release this as a kit or ready assembled unit?

[lliont]

Thanks
After I finalize the firmware I will make a few for start, for anyone that wants one. I have 9 pcb but I have parts to make only one more so I have to order.
I made a 4-layer pcb this time. It works as expected with no problems at all so far.

https://drive.google.com/file/d/1OAYBhD ... 2TQFF/view

[Peter]

May I kindly ask why you are using those totally obsolete EPM7160 chips for a new design? They are so rare that I could not find any European source below 60 € per chip. Wouldn't a newer 5V tolerant chip with 3.3V supply also be suitable? It's just an LDO to add, and your PCB is not so small that it would be a space problem. Is it for technical reasons like slewrate? Or because you are familiar with the EPM7000 series?

Great job anyway!

[lliont]

Hi Peter, because it works and I'm lazy

Make a suggestion of a new 5V tolerant and of the same size/price cpld and I'll try it. 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.
Currently EPM7160S are available from ebay sellers, 10€.

Since I was still devloping new features I wanted to be sure that if something went wrong was not because of an unpredictable factor but because of my doing.
Now that I know it works I can try it.

I have one extra pcb assembled and tested but without the pal encoder for the extra composite output soldered, if someone is interested send a pm.