Search found 1298 matches

by Pr0f
Fri Jan 12, 2024 9:55 pm
Forum: Compatibles Corner
Topic: ICL OPD
Replies: 180
Views: 166831

Re: ICL OPD

There were some second source makers for these chips - such as VLSI - VL1772 - and I think there was a couple of versions that were practically interchangeable too 1771 if memory serves.
by Pr0f
Fri Jan 12, 2024 5:48 pm
Forum: Compatibles Corner
Topic: ICL OPD
Replies: 180
Views: 166831

Re: ICL OPD

On some of the retro brew projects I've seen those as low as 300 Ohms - but that's with a different floppy controller that drives quite a high current - the LS TTL chips are probably not going to want to see that low a load. I suspect the decoupling capacitors should be 100nF as that's almost a stan...
by Pr0f
Fri Jan 12, 2024 5:42 pm
Forum: Compatibles Corner
Topic: ICL OPD
Replies: 180
Views: 166831

Re: ICL OPD

It's just I seem to have more of them than the 1.44MB variety - lol
by Pr0f
Fri Jan 12, 2024 3:25 pm
Forum: Compatibles Corner
Topic: ICL OPD
Replies: 180
Views: 166831

Re: ICL OPD

Derek_Stewart wrote: Fri Jan 12, 2024 2:31 pm Hi,

Do you have the main board schematics, maybe a a new PCB could be made.
Derek - Stephen posted the KiCad files in the thread earlier :-) But note the issue with the clock generator and fix for this.
by Pr0f
Fri Jan 12, 2024 2:14 pm
Forum: Compatibles Corner
Topic: ICL OPD
Replies: 180
Views: 166831

Re: ICL OPD

time to unearth my stash of 3.5" DD floppy drives :-) I am sure I've got some 5v only ones too - unless they are HD, not that I would try and power the drive from the dongle, but I am thinking of putting the floppy in the box I use for the power supply and QLPICO VGA interface.
by Pr0f
Fri Jan 12, 2024 12:59 pm
Forum: Compatibles Corner
Topic: ICL OPD
Replies: 180
Views: 166831

Re: ICL OPD

Thanks Stephen - I shall download that later and have a look at the code. I noticed that in circuit - the DDEN pin is grounded on the WD1772, in QL disk interface designs - this is often fed from a latch so the density can be controlled - do you know off hand what density this interace uses - is it ...
by Pr0f
Fri Jan 12, 2024 7:30 am
Forum: Compatibles Corner
Topic: ICL OPD
Replies: 180
Views: 166831

Re: ICL OPD

I was thinking about the possibility of reduction - I think you could get away with:

Crystal oscilator
WD1772
A GAL - possibly even just 16V8 size
An LS240 or equival(for buffering disk drive signals)
An Eprom / Flash
An LS174 / LS175 latch

It's teasing my brain now :-)
by Pr0f
Thu Jan 11, 2024 10:37 pm
Forum: Compatibles Corner
Topic: ICL OPD
Replies: 180
Views: 166831

Re: ICL OPD

Many thanks for sharing this and the hard work in reverse engineering it.

Do you have the ROM code available?
by Pr0f
Thu Jan 11, 2024 10:35 pm
Forum: Compatibles Corner
Topic: ICL OPD
Replies: 180
Views: 166831

Re: ICL OPD

Actually - I just noticed it's marked all your capacitors as 1pF. I think I get the circuit now, and I think I know why it might not be oscillating - the 2 74LS04's that are wired around the crystal should have some feedback resistors between input and output - this will bias them into the linear mo...
by Pr0f
Thu Jan 11, 2024 10:05 pm
Forum: Compatibles Corner
Topic: ICL OPD
Replies: 180
Views: 166831

Re: ICL OPD

Trying to understand the circuit around the crystal, it looks like a 1pF capacitor in the feedback loop with the crystal?