Talywain wrote: ↑
Tue Jan 08, 2019 7:18 pm
Wow. You’ve been busy. As for the disk busy signal, could it be a density select issue i.e 360 KB low density, 160 KB single sided and 1.2 MB high density.
I've just skipped through the Interface Age PDF you linked to and it's a very nostalgic thing. Especially the advertisements. I think this period of computing was the most interesting; the proliferation of machines, peripherals and software was indicative of a rapidly expanding industry. Maybe that is why we all think of it as a special time.
Regarding SBII board progress, a degree of enthusiasm helps! Plus, I have the Intertec schematic pack which covers this board and the previous Superbrain I as well as the other modules (like the hard disk adapter). Once I have it booting I am planning to build a case for it, but as ever the electronics come first.
The boot ROM (which has a label on it: "SB II SB4.2", a reference to the ROM version (which matches what it prints in the screen memory at start up). This is the latest ROM I have seen (4.003 being the previous most recent) and I will dump it and upload to VCF, where there is a thread that discusses SB ROMs. It appears to be intact - SBs seem to be susceptible to bit rot in their boot ROMs, maybe because they are unusual TMS2716 parts.
The drives connected are DS/DD 3.5" but I also tried with SS/DD 5.25" as well. It didn't occur to me that this might be a Superbrain II SD (they were named JR, QD and SD in ascending order of drive capacity) but it has an SAB 1793 FDC which is SD or DD capable, so I think disk density is not a problem here. I'm using a DS/DD disk and it should be able to read the boot tracks at least.
There is a discrepancy here. The Intertec schematic says the FDC should be an SAB 1791 and the data sheet says the difference between that and a 1793 is that the 1793 uses an inverted databus. So I'm going to swap it out for a 1791 first. Probably won't help but let's see..
[Edit: No, still waiting for busy. So the FDD wasn't the problem.]