Post
by stephen_usher » Fri Jun 21, 2019 9:35 pm
Well, I managed to get a 'scope onto some of the lines on the NetUSBee.
The data bus signals look nice and square. On the address bus, however, although many are nice and square others look like shark fins, just about reaching 5V by the end of the pulse. Those aren't going to work well! So, yes, it looks like a pull-up problem.
I bet your bottom dollar this is the reason why it (and the Spectre GCR) don't work on the TT too.
I'm wondering how feasible it would be to add pull-up resistors into the address lines on the cartridge. I've no way of making a PCB with a male edge connector and female edge connector.
P.S. I'm guessing that the old PSU had slightly higher voltage on the +5V rail which meant that the voltage rose more quickly, getting to the TTL high value fast enough for things to just about work.
Intro retro computers since before they were retro...
ZX81->Spectrum->Memotech MTX->Sinclair QL->520STM->BBC Micro->TT030->PCs & Sun Workstations.
Added code to the MiNT kernel (still there the last time I checked) + put together MiNTOS.
Collection now with added Macs, Amigas, Suns and Acorns.