ZX8301 replacement for Sinclair QL

Having burned two ZX8301 chips in the last years was a motive to make a cpld based replacement for the QL ZX8301 ULA.

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After reading Nasta's description of the ZX8301 ULA I programmed an Altera EPM7160S cpld in VHDL and made a pcb that replaces the ULA.

These PLCC versions fit in a QL with soldered ram chips but I don't think they fit a repaired QL with socketed rams, so I made also a smd cpld pcb that will fit in those QLs too.

I now managed to fit the ULA to a smaller EPM7128S cpld with all the functionality in both PLCC and SMD versions, so I ordered new pcb from PCBWay, see project logs.

Everything functions ok, I tested it also with a couple of cards.
One has to be very careful to choose the correct pins that will fit in the ULA socket so that they fit correctly and are not too thick and damage the socket.
Few times you have to power the QL twice to boot correctly and I try to find out why this happens. It then works without any problem even if you reset it.

The cpld used is a EPM7160S, the PLCC84 package version  (EPM7160SLC84-10, EPM7160SLI84-10 ) or the smd EPM7160STC100-10.

Other components needed are:

one 74LS241 or 74LS244 the smd package.

6 x 100nf smd 0805 capacitors.

one 30Mhz active crystal oscillator smd

one plcc 84 pin socket

2x5pins header for the programming port (that I don't solder on the pcb, I just lightly and partially sideways press in the holes as long as the programming lasts).

And 40 thin pins (2x20 header) to solder on the pcb that will fit in the original ULA socket, these pins should be thin enough not to damage the socket.

other pcb components that are optional (not really needed):

1x 10uf electrolytic low profile capacitor

4x 10K smd 0805 resistors

There is also an option to output the flash bit signal at JP2 when JP1 is pulled hi to be used for other purposes (more colors). This will disable the standard flash behavior.

Caution!, For the new SMD cpld pcb this changed, JP1 is the output and JP2 must be pulled hi.

WARNING: build this project at your own risk. I tested it on (2) issue 5 QL's and with 2 cards (qubide and Micro Peripherals floppy controller), one at a time and with both of them attached. 


EPM7160S 100pin SMD CPLD program

pof - 9.82 kB - 11/23/2022 at 19:48


SMD CPLD PCB production files

x-zip-compressed - 14.43 kB - 10/23/2022 at 07:07



EPM7160S 84pin PLCC CPLD program

pof - 9.82 kB - 09/24/2022 at 14:30


PLCC CPLD PCB production files

x-zip-compressed - 15.83 kB - 09/24/2022 at 14:28


  • New pcb using the EPM7128STC100 smd IC

    Leon11/22/2022 at 12:53 0 comments

    Received the new PCBs for the EPM7128STC100 smd version from PCBWay.

    I use PCBWay for my project's pcb production and I am very satisfied with the results, I always get perfect pcbs with very fast production and delivery times and low cost. See this article for more info about the PCBWay service quality.

    I am waiting for the EPM7128STC100 ic I ordered and soon I'll test the new design that provides extra RGBs outputs with mixing of the flash bit for 16 colors. After testing I'll publish the new pcb data.

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