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CPLD replacement for ZX8301
Posted: Fri Jun 17, 2022 11:23 am
by bwinkel67
Theodoulos Liontakis posted on the Sinclair QL For Everyone Facebook group that he has successfully created a CPLD replacement for the ZX8301.
This link will likely not work unless you are a member of the group:
https://www.facebook.com/photo/?fbid=54 ... 4457487075
Here is a picture:
Re: CPLD replacement for ZX8301
Posted: Tue Jun 21, 2022 11:09 pm
by lliont
It works with everything I have tested (not much) including my version of qubide card (832K ram) and the Micro Peripherals floppy controller.
I haven't implemented the flash bit because I can't fit it in EPM7128S CPLD, but I have ready the code for a EPM7160 CPLD and waiting for the ic I ordered from China to test it.
I made a new pcb that will work with either 7128S or 7160S and also has a buffer for the video signal for better quality but I haven't ordered it yet.
Re: CPLD replacement for ZX8301
Posted: Tue Jun 21, 2022 11:45 pm
by mk79
Pretty cool, well done. I've started doodling something similar a while back with a XC95144XL but as I got a ton of replacement ZX8301 I never felt the need to finish it
Then I was thinking about doing a FPGA version that directly outputs a VGA signal but that makes it a lot more complicated and with current chip prices it's no fun anyway.
Re: CPLD replacement for ZX8301
Posted: Tue Jun 21, 2022 11:56 pm
by bwinkel67
I've found ZX8301's hard to find. I located one source (Mutant Caterpillar) for a reasonable price, but glad a replacement is out there.
Will this become an open source project (github) once complete?
The ZX8302 it the other custom chip that hasn't been recreated, correct?
Re: CPLD replacement for ZX8301
Posted: Wed Jun 22, 2022 12:25 am
by lliont
Maybe I'll make it public, not sure about the source code, maybe just the CPLD programming file and the pcb.
Re: CPLD replacement for ZX8301
Posted: Wed Jun 22, 2022 12:47 am
by M68008
lliont wrote:also has a cd4050 buffer for the video signal for better quality but I haven't ordered it yet.
Would video output also benefit from ESD protection?
Re: CPLD replacement for ZX8301
Posted: Wed Jun 22, 2022 1:03 am
by lliont
M68008 wrote:
Would video output also benefit from ESD protection?
Even if something gets damaged from ESD it would be a cheap chip
The reason I add the buffer is a flicker I noticed in the 256x512 mode in some patterns and I think the buffer can drive the video outputs better.
By the way if someone has to suggest of a suitable video buffer (but cheap and easy to get) please do, I haven't ordered the pcb yet so I can still make changes.
I have a lot of 74LS241 buffer/line drivers -15/24ma, 12ns, 133 Ohm load maybe those are ok, I'll see.
I'm sure the LS chip is less sensitive to ESD.
Re: CPLD replacement for ZX8301
Posted: Wed Jun 22, 2022 1:37 pm
by lliont
bwinkel67 wrote:I've found ZX8301's hard to find. I located one source (Mutant Caterpillar) for a reasonable price, but glad a replacement is out there.
If you live in UK the price is reasonable, I live in Greece and a ZX8301 from ebay with price 35 pounds cost me 62 pounds after customs (Brexit) and shipping fees.
With that amount I developed the replacement, with about double the sum I could have bought another QL maybe.
Re: CPLD replacement for ZX8301
Posted: Wed Jun 22, 2022 3:35 pm
by Derek_Stewart
Hi,
I would prefer the CPLD replacement then the code could modified, rather than fixed chip.
Could I make one myself?
Re: CPLD replacement for ZX8301
Posted: Wed Jun 22, 2022 9:16 pm
by lliont
I'll inform when I finish and test the next-better version.