Search found 624 matches

by Pr0f
Sun May 17, 2020 6:19 pm
Forum: Hardware
Topic: QL Eprom programmer
Replies: 36
Views: 7198

Re: QL Eprom programmer

Anything and everything welcome :-)

It's a slow burner project, but I liked my old QEP 3, and it would be nice to put another QEP like programmer back out there...
by Pr0f
Sun May 17, 2020 1:10 pm
Forum: Hardware
Topic: All RAM chips destroyed??
Replies: 95
Views: 15732

Re: All RAM chips destroyed??

For most of the CPU lines, they are only connected to at most about 4 devices - A15 for instance, goes to one of the 257 mux inputs and to the 2 ROMS - and to the expansion and ROM sockets. Only 3 devices. Similar story for most of the lines. In the technical manual for the QL it does stipulate that...
by Pr0f
Sun May 17, 2020 10:16 am
Forum: Hardware
Topic: All RAM chips destroyed??
Replies: 95
Views: 15732

Re: All RAM chips destroyed??

But with nmos, signals are pulled low - so that's ok :-)
by Pr0f
Sun May 17, 2020 9:54 am
Forum: Hardware
Topic: All RAM chips destroyed??
Replies: 95
Views: 15732

Re: All RAM chips destroyed??

DC Table:
68k_dc_table.png
by Pr0f
Sun May 17, 2020 9:48 am
Forum: Hardware
Topic: All RAM chips destroyed??
Replies: 95
Views: 15732

Re: All RAM chips destroyed??

Is it right that the 68008 address lines can only source 400uA because if so they should be buffered before going on to other things. An LSTTL input can take 100uA and I don't know what the two ROMs take then the lines leave the board via ROM and expansion connectors that is asking for trouble sinc...
by Pr0f
Sat May 16, 2020 3:05 pm
Forum: Hardware
Topic: Issue 6 VM12 & resistors confusion
Replies: 79
Views: 4344

Re: Issue 6 VM12 & resistors confusion

Resistors on a bus like that in that sort of value range are more likely to be there to prevent ringing or overshoot on the bus lines due to long copper runs and associated capacitance / inductance.
by Pr0f
Sat May 16, 2020 12:09 pm
Forum: Hardware
Topic: Issue 6 VM12 & resistors confusion
Replies: 79
Views: 4344

Re: Issue 6 VM12 & resistors confusion

If your eprom is hosting the Minerva OS that's giving you those numbers, then I would suggest it's ok - the problem lies with RAM / Transceiver / ZX8301, but most likely a failing RAM chip...
by Pr0f
Fri May 15, 2020 2:43 pm
Forum: Hardware
Topic: All RAM chips destroyed??
Replies: 95
Views: 15732

Re: All RAM chips destroyed??

Not sure if it matters, but NatSemi is part of TI today. (Would that mean the Service Manual warning extends to TI now? Tobias It would be interesting to know the reason for that parituclar requirement, as there are so many more manufacturers of logic and also now new logic families, like HC, HCT e...
by Pr0f
Fri May 15, 2020 12:13 pm
Forum: Hardware
Topic: All RAM chips destroyed??
Replies: 95
Views: 15732

Re: All RAM chips destroyed??

It was the 74LS257 (and the 74LS245) in the service manual that had a chip source / manufacture note:

IC19,20 74LS257 As NOT Nat. Semi
IC21 74LS245 Issue 5 NOT Nat. Semi

So not National Semincondutor version...
by Pr0f
Fri May 15, 2020 12:05 pm
Forum: Hardware
Topic: All RAM chips destroyed??
Replies: 95
Views: 15732

Re: All RAM chips destroyed??

sometimes faster can be a problem - if someone has relied on a more latent signal that a particular manufacturer has, then using a chip with faster timings won't work. It's not really good design practice to do that anyway - should always design for worse case - but that wasn't always Sinclair's sty...