I'm crap at analog electronics stuff so I didn't even think about that

Also, if you use a positive-AND, such as a 74xx08, instead of the NAND followed by the inverter, your circuit will be more responsive to IRQs (two gate delays with your present arrangement vs. one), which may be important with a UART such as the 6850, as it has no FIFOs.

Thanks for the advice BDD ...

Thank you BigEd, from memory I remembered it as being "TTL compatible". Going back to the data-sheet after your reply I saw that it was "TTL compatible, open-drain (no internal pullup)". So I added a 3.3k resistor on the back of the pcb to pin 10 and 5v and now it's working fine.

Can somebody tell me what is wrong with this? VIA_IRQ is from a WD65C22 (S variant), ACIA_IRQ is from an MC68B50P and IRQ is connected to the WD65C02's interrupt pin. If I jumper either of the irqs to the output of the inverter then that interrupt goes thru to the processor. As wired, the IRQ line ...

I had no luck with the GAL22V10D with this programmer

Well, I tried it out this morning, hoping that maybe the reading back/verify portion of the programmer was just crapping out. No such luck... It's just not working past the 32nd. I have been debating wether to get the Genius programmer, another £30-£40 and the wait for the slow boat from China, but ...

I tried that too, program with no verify, it completed the cycle but from a visual inspection it did not do it correctly which then doing the verify confirmed. Thx i_r_on for confirming it's not just me doing something wrong.

I was using an older version, I updated after the failed burn. I'm on Win7 and yes, out of frustration I have tried the B and C types to no avail.

@ cbscpe
No generics I can select Lattice GAL22V10 B, C or D and then DIP or @SOIC24.

@i_r_on
I've just re-attached the pld file after adding a .txt so that it would upload. That is the other unkown quantity... In WinCUPL there is only the B and C versions. Looking at other's code they use g22v10 ...

Hmph! Just tried a fresh GAL, the closest Vpp options I have are 12.50v and 13.50v, tried the lower value first then the higher value. Both had the same result stopped at byte 32 unable to verify as before.

It's a Lattice GAL22V10D 15LPN the rest, I believe is batch# and date - G306DE27

Okay, I decided on the weekend to replace the TTL with a GAL22V10D before I finalize the PCB. So I downloaded winCUPL and went thru the tutorial - not exactly rocket science so I create my own .pld file. And the fun begins... Doing the tutorial I could run a simulation of the result. With my file it ...

Now that is more like it - a one chip solution, I had a look on RS and Farnell, not a DIP package in sight... sigh.... I'll keep looking though for an adapter so I can use one on a bread board.

hey thx Garth, that looks doable. Are the caps okay being ceramic or should I use a mylar or other?

First!

As in, my first post, and also: when you come across an odd frequency like this, the first thing to do is to check if it is a multiple of some common frequency, or if there is a common frequency that is a multiple of it. Then check a list like this one in case you missed it.

Nice list ...