Search found 5034 matches

by 1024MAK
Sat Feb 24, 2024 3:40 pm
Forum: Welcome Area
Topic: Hello from Poulette73
Replies: 7
Views: 303

Re: Hello from Poulette73

I can take one and post it up later today.

Mark
by 1024MAK
Sat Feb 24, 2024 11:14 am
Forum: Welcome Area
Topic: Hello from Poulette73
Replies: 7
Views: 303

Re: Hello from Poulette73

Hello and welcome to our forum Olivier! :D :D :D I hope you enjoy this forum :D You are welcome to ask questions! With respect to the modulator / video circuitry, it's recommended to take the video feed for the composite video board from pin 16 of the ULA from the underside of the board. If removin...
by 1024MAK
Thu Feb 22, 2024 12:37 am
Forum: Hardware
Topic: ZX81 toZX80 conversion.
Replies: 11
Views: 424

Re: ZX81 toZX80 conversion.

@Moggy, it's all white mate :lol:

Mark
by 1024MAK
Wed Feb 21, 2024 9:11 am
Forum: Hardware
Topic: I've borked it
Replies: 112
Views: 2751

Re: I've borked it

I've compared the Hitachi chip against the half K chip read cycles and it looks like /OE is doing nothing. Looks like the whole thing is driven by the /CE and I should instead tie /OE to ground? Or do I have that wrong? Wrong. /CE (/CS) when low selects the chip and if it has a lower power standby ...
by 1024MAK
Tue Feb 20, 2024 11:07 pm
Forum: Hardware
Topic: 16k Sinclair issue 1 pack
Replies: 8
Views: 253

Re: 16k Sinclair issue 1 pack

Photos in this topic please. Also send copies to me via email (see my PM) :D

Hi-res mod for a 16K RAM pack, see this topic ;)

Mark
by 1024MAK
Tue Feb 20, 2024 10:14 pm
Forum: Hardware
Topic: 16k Sinclair issue 1 pack
Replies: 8
Views: 253

Re: 16k Sinclair issue 1 pack

Sinclair (and most other brands/makes) 16K RAM packs that use DRAM chips normally need a modification for full Hi-Res graphics to work correctly. I thought we had some photos of an issue 1 RAM pack, but either I was mistaken, or I just can't find them... (we do have photos of issue 2 and issue 3 tho...
by 1024MAK
Tue Feb 20, 2024 9:52 pm
Forum: Hardware
Topic: I've borked it
Replies: 112
Views: 2751

Re: I've borked it

This is why I'm confused as well...

Mark
by 1024MAK
Tue Feb 20, 2024 9:48 pm
Forum: Hardware
Topic: I've borked it
Replies: 112
Views: 2751

Re: I've borked it

No, if you make use of the /RD line, that messes up hi-res graphics. With very slow RAM, it makes a difference if /OE and /CS (/CE) are controlled differently. But with 'normal speed' chips, the RAM chip should be fast enough that the chip will respond in plenty of time, hence no problem with /OE an...
by 1024MAK
Tue Feb 20, 2024 7:24 pm
Forum: Hardware
Topic: I've borked it
Replies: 112
Views: 2751

Re: I've borked it

Yes, fitting extra 100nF multilayer ceramic capacitors (as close as possible to the power pins of the chip) is wise. But I'm not convinced this is the issue here. The ZX81 does have four 47nF ceramic capacitors, which given the size of the board, is at least something. C9, one of these four is near ...
by 1024MAK
Mon Feb 19, 2024 6:54 pm
Forum: Hardware
Topic: I've borked it
Replies: 112
Views: 2751

Re: I've borked it

My fear is that the original Ferranti ULA and both vLA81 modules have had their pin 12 outputs damaged some how. With R2, all the above should have no difficulty producing a logic high voltage on their pin 12. As this is a logic level output, it should either be driven high, or when the Z80 is tryin...