ZX81 ULA-in-a-CPLD

[McKlaud]

Andy, nice features

[Andy Rea]

little update second prototype PCB arrived and i have built one up, a little tweaking with the tape inout circuit and all is well.
top side:

bottom side ( still ocvered in flux )


tape input works reliably with my Timex branded cassette player i can load programs with volume between 5 and 7... with a " perfect source " OTLA found here https://code.google.com/archive/p/otla/ i can load 3D monster maze in as little as 9 seconds, with windows volume anywhere from 50% to 90% OTLA works surprisingly well.

The 2 other proto boards will be built ( and cleaned ) in the next few days and after testing, a couple of lucky forum members will be gifted these boards for further testing / evaluation / end user experience blah blah....

If all goes well i will order a larger quantity of boards and get building.

Regards andy

[Lardo Boffin]

If all goes well i will order a larger quantity of boards and get building.

Regards andy

I couldn’t see an ‘excited’ smiley.

[McKlaud]

I am impressed with your progress, Andy. Well done and the board looks stunning.

[1024MAK]

IMG_7073.JPG (26.73 KiB) Viewed 7210 times

He drooled uncontrolledly as he typed the message...

Lovely work there, well done Andy

Mark

[Moggy]

Looks good,Andy and it also means longevity for our zeddies as it will replace this most important yet obsolete component.

[nollkolltroll]

Very nice to have some proper replacement for our aging HW.
Any plans for further functions, like a super ULA?

[TMAOne]

Congratulations Andy!

This is truly a milestone in Zeddy history, as I know many otherwise good examples have gone to the dumpster for lack of a replacement ULA.

Good going. I look forward to them being widely available.

[Andy Rea]

built the other 2 this evening and after testing both worked as expected, i then tried one inside a real zx81 case... oh my the link in the middle is mighty close to touching the case ... the easiest thing would be to fit a right angle header. (might have to bend it up slightly ) the link is there to add a 75 ohm load should you be unlucky enough to own a monitor / tv that has a high impedance input.....

On second thoughts looking at the picture again i could just lose the plastic bit on the bottom of the pins so when fitted the shorting link would sit on the PCB. that would easily provide more than enough clearance.



isnt it funny how the colour of the caps change with the angle... c1, c5, c6 ,c9 are all the same ( from the same strip )



the eagle eyed may notice that pin 35 does not have a SIL pin in it, this is now an input that can be left unconnected for standard operation or grounded to enable M1NOT operation.

so erm yeah.... thats it for now....

Very nice to have some proper replacement for our aging HW.
Any plans for further functions, like a super ULA?

Not at this time other than M1NOT and that happened as an afterthought and then only because i am using on board oscillator so have a pin free.

Regards Andy

[McKlaud]