t0nyt wrote: Sun Jun 02, 2024 6:02 pm
You can't do anything that needs the Microdrives as Q-emuLator doesn't support the 68K/OS MD format yet (but I believe Daniele is working on that from a logic capture of my drive)
Yes, I have a prototype that allows 68K/OS to access the microdrive:
GST_screen1.png
Still thinking about the mdv image format, it's ... complicated.
I've also noticed that the ICL OPD microdrive cartridges have a sub-byte space between block header and sector data, so I wonder whether a byte-based representation would work well for them.
I was always intrigued to use the 68K/OS system but i never had the rom board. Reading this thread i decided to burn 27512 eproms and use theme on a minerva pcb adapter. So I programmed one 64kb eprom, first 32kb part at (0000hex) with OS bin file and the next 32kb part at (8000hex) with the Utils bin file. The only difference with the second eprom is that the utils bin file is the 16kb, programmed at C000. I don't know much how to use the OS, but i seems to run ok, as you can see at photos. I will try to mofify a rom port cartridge pcb, for use with 27512 eproms as Chr$ mentioned but it will take a while as the cartridge pcb has a different layout.
I tried to fit a 32K EPROM of the OS inside my test QL today (in place of JM ROMs), but all I get are black and white stripes (despite the eprom verifying multiple times)
Luckily when I re-fitted the GST 68K/OS card the QL was still working so I haven't damaged anything it seems
I obviously have more to learn about what EPROM's will work in a QL!
Could anyone explain to me, in laymen terms, why this 32K eprom is no good please? (I can use the 16K ST 27128AF1 EPROMs ok)
As per my previous post - the OE signal on the Eprom is active low - and on the QL PCB - and hence on the ROM socket - it's active high.
You will need to invert the signal with a transistor or a logic gate.
Easiest would be to use a BS170 mosfet - gate to the ROMOEH signal on the QL socket, Source connected to Ov, and the Drain connected to the OE pin on the Eprom and to a resistor of say 2K7 to 5v line - this ensures the chip is not selected when the ROM is not being accessed.
Pr0f wrote: Thu Jun 06, 2024 4:42 pm
As per my previous post - the OE signal on the Eprom is active low - and on the QL PCB - and hence on the ROM socket - it's active high.
You will need to invert the signal with a transistor or a logic gate.
Easiest would be to use a BS170 mosfet - gate to the ROMOEH signal on the QL socket, Source connected to Ov, and the Drain connected to the OE pin on the Eprom and to a resistor of say 2K7 to 5v line - this ensures the chip is not selected when the ROM is not being accessed.
Thanks Pr0f, I’d misunderstood re using a single 32k eprom.
What you describe is way above my pay grade currently unfortunately
Hopefully Chr$ will have some luck building me a plug in board
Chr$ wrote: Tue Jun 04, 2024 7:28 pm
You can also modify those boards to take a 64k 27C512 chip and replace the entire internal ROM(s) and have the C000h area for whatever you want.
It looks like this:
20240604_202557.jpg
Hopefully you can see the cut traces etc.
Oh, that's pretty neat. Has anyone created replacement PCBs that implement this 64K variant of the ROM boards? Pretty handy to be able to throw whatever combination of OS and add-on and plug it into the ROM socket instead of having to open up the machine.
ones' complement wrote: Thu Jun 06, 2024 9:53 pm
If only ROMOEH had been like ZX ROMCS and could be usurped. Need to remove internal ROMs to put 64K on ROM port.
It's a pity they couldn't have employed the unused ROM port pin, we could have had 16K ($C000-FFFF) / 64K ($0000-FFFF) option. With true ZX8301 ROMOEH output wired to ROM port and internal ROMs ROMOEH conditioned by spare pin: grounded for 64K, open for 16K.
I suppose it's not impossible to do a mod to that effect now but I guess QIMSI has bagged that pin now
