Oh no! Not another ULA.

[Andy Rea]

You mean either side of R28…
One side is connected to the ULA.
The other side is connected to the edge-connector and (on a standard machine) to the ROM.

But I presume on a modified machine, the output of the OR gate will drive the ROM instead.

Because the OR gate has one input directly connected to the ‘ULA’, the thinking is that it will switch fast enough?

Why do you think you need a pull-down resistor? A high value would not make much difference as if I understand you correctly, it’s still getting a signal via R28 (680Ω), admittedly very slightly delayed due to stray capacitance. But a low value would draw rather a lot of current.

Mark

no R28 removed from circuit. so ula romcs is only going to ore gate, and romcs from edge is only going to other input and cs at internal rom is directly from or gate output and not connected to any other part of circuit.

what if machine is used without anything connected to edge connector what value will input to or gate see ? i don't want to disable internal rom when nothing connected to edge connector.

and yes to improve the signal integrity and gain a some nano seconds.

[Andy Rea]

My guess is he wants to short R28

Remove completly.

[1024MAK]

If R28 is removed, yes, you will need a pull-down resistor. I presume you will not be using 74xxx, 74LSxxx or 74ALSxxx logic, but more modern fast logic.

Mark

[Paul]

Maybe inside the CPLD?

[Andy Rea]

Maybe inside the CPLD?

yes this probably, heck if your already soldering half a dozen extra wires for additional features, changing your rom to a faster one, and possibly your ram ( whoever is still using internal 1 or 2K ) then heck a few more wires ain't gonna hurt.

Andy

[Paul]

[Andy Rea]

Quick update for what it's worth...

Crap happens... My personal circumstance has changed somewhat.

Project on hold until further notice.

Regards Andy

[Moggy]

Understood Andy, Take care buddy and keep in touch.

[Paul]

Thanks for the update. Charlie already told me some weeks ago.
Please keep in touch.
And good luck for your personal circumstances.
Cheers
Paul

[1024MAK]

Understood Andy, Take care buddy and keep in touch.

What he said. Look after yourself and your family.

Mark