Search found 107 matches

by Rishi
Sat Aug 15, 2015 2:09 am
Forum: Hardware
Topic: Trying to restart a 33 years old ZX81 [SOLVED]
Replies: 54
Views: 19713

Re: Trying to restart a 33 years old ZX81

if you don't have an oscilloscope, my test-pen could also be used as an indication of pulse (mind you not as continues pulse as an oscilloscope does) it can indicate if a pin goes either high or low at times, and is a lot cheaper to make (and i mean a lot cheaper the switches cost the most)
by Rishi
Sat Aug 15, 2015 2:03 am
Forum: Sinclair Misc
Topic: Zaks book error ?
Replies: 12
Views: 4683

Re: Zaks book error ?

ehm Mark do you have a clear copy of page 170 as well, the PDF is just to grainy.
by Rishi
Thu Aug 13, 2015 9:46 am
Forum: Sinclair Misc
Topic: Zaks book error ?
Replies: 12
Views: 4683

Re: Zaks book error ?

Thanx again, that is clear it is as i thought it was and i do not need to revise my way of thinking...
by Rishi
Thu Aug 13, 2015 12:30 am
Forum: Sinclair Misc
Topic: Zaks book error ?
Replies: 12
Views: 4683

Zaks book error ?

when i recovered our ZX81 i also looked for the book i bought (on special order) Programming the Z80 by Rodnay Zaks, but i didn't manage to find it back, fortunately it was available online as PDF (also 2nd hand for about $50 + postage and handling, but that was a bit to much, i can buy a Kindle for...
by Rishi
Tue Aug 11, 2015 1:41 am
Forum: Hardware
Topic: Memopak : bad RAM chips ?
Replies: 96
Views: 33279

Re: Memopak : bad RAM chips ?

that was what i was doing, but anyway i'll get back onto the subject later.
by Rishi
Mon Aug 10, 2015 10:13 pm
Forum: Hardware
Topic: Memopak : bad RAM chips ?
Replies: 96
Views: 33279

Re: Memopak : bad RAM chips ?

Yes, yes, of course i think the schematic is somewhere earlier in this thread,
but i mean i tried the 1K Hires in 1K mode, isn't it supposed to work ? or do i need to mod that as well, maybe i misread that somewhere that it just works in 1K.
by Rishi
Mon Aug 10, 2015 8:03 pm
Forum: Hardware
Topic: Memopak : bad RAM chips ?
Replies: 96
Views: 33279

Re: Memopak : bad RAM chips ?

Well when i had it on the breadboard, i had !RD directly on the !RD on the RAM, but that didn't work, hence checking to make sure that !RD || !MREQ, both have to go low before the pin on the RAM goes low, and that did work. Any idea why the 1k Hires marble racer didn't work ?
by Rishi
Mon Aug 10, 2015 3:08 am
Forum: Hardware
Topic: Memopak : bad RAM chips ?
Replies: 96
Views: 33279

Re: Memopak : bad RAM chips ?

Well at the moment i've got it wired up (!MERQ || !RD) -> RD(on Ram) i'm using standard C++ logic notation just to make sure no confusion occurs. Of course this works, but not for HiRes, so the plan was to change that to (!RFSH && !RD) || !MERQ -> RD(on Ram) I've never had HiRes working on my ZX81, ...
by Rishi
Sun Aug 09, 2015 11:02 am
Forum: Hardware
Topic: Memopak : bad RAM chips ?
Replies: 96
Views: 33279

Re: Memopak : bad RAM chips ?

Thank you Mark, there was some confusion, at least i had it clear it clear in my head but Pokemon's answer confused me a little but now it is clear, also where to put the active-low OR-gate, or an actual AND-gate, cause i think that's what i'll put. The cycle-map makes it all clear. this is not goin...
by Rishi
Sun Aug 09, 2015 2:00 am
Forum: Hardware
Topic: Memopak : bad RAM chips ?
Replies: 96
Views: 33279

Re: Memopak : bad RAM chips ?

Hold on ! Ok, we have 300ns that's heaps, a lot more then I thought anyway, but eh OR-ed ? either one of them has to go low for a RD request doesn't it ? if i use an OR gate they'd both have to go low before it goes low, or not ? it's the inversion that makes this stuff so tricky, atm i have !RD on ...