forum.defence-force.org

@kenneth. A proposal to improve Erebus for future batches . You only need to add a resistor and, of course, modify the PCB.

Indeed, using the three state output coud be a good solution for the open collector problem, it could be added with the reset button update.

I like that hack

It's even better than the diode thing, as it's a proper TTL drive output, either drive the line low, or leave it to float (open).

As noted in another posting, this sort of thing needs to be done on any other thing on the IO control line though (because a.n.other device may drive the line HIGH, while this one pictured is driving LOW, and you still have a conflict).

mikeb wrote: ↑Sat Jun 20, 2020 4:33 pm... As noted in another posting, this sort of thing needs to be done on any other thing on the IO control line though (because a.n.other device may drive the line HIGH, while this one pictured is driving LOW, and you still have a conflict).

Correct! For this reason I said in the RetroWiki forum, that from now, we all must design the interfaces thinking about a shared bus.
We should to use open collector/drain or Tri-state outputs on /MAP, /ROMDIS, /IRQ, /I/O_CTRL and /RESET lines.

Silicebit. wrote: ↑Sat Jun 20, 2020 6:20 pm

mikeb wrote: ↑Sat Jun 20, 2020 4:33 pm... As noted in another posting, this sort of thing needs to be done on any other thing on the IO control line though (because a.n.other device may drive the line HIGH, while this one pictured is driving LOW, and you still have a conflict).

Correct! For this reason I said in the RetroWiki forum, that from now, we all must design the interfaces thinking about a shared bus.
We should to use open collector/drain or Tri-state outputs on /MAP, /ROMDIS, /IRQ, /I/O_CTRL and /RESET lines.

We must add the fact that we will also have to choose the interface working area on page 3 and in the ROM area.

Silicebit. wrote: ↑Sat Jun 20, 2020 6:20 pm We should to use open collector/drain or Tri-state outputs on /MAP, /ROMDIS, /IRQ, /I/O_CTRL and /RESET lines.

Open-collector and tri-state are not the same.

Open-collector basically creates an AND gate with all participating outputs, so any one setting it to 0 will get a 0 on the line.

Tri-state is just a way to temporally multiplex regular totem-pole outputs on the same line, but if you don't have a proper arbitration logic you will screw up anyway at some point. Can you be sure no-one will ever create a hardware that uses the same address as you, but with different timings when asserting IO_CONTROL?

As for the diode, I already explained this might or might not work depending on the ORIC and the diode you put in.

I just checked what the Jasmin does, it uses a 74LS38 (Quad 2-input NAND Buffer (Open Collector)) for /MAP, /IO_CONTROL, /IRQ, /ROMDIS and /RESET, with the second input to a pull-up or down. The inputs must be reversed obviously.

It's hard to be a good citizen on the bus

Although, in the case of peripherals using the same IO they will end up having trouble on the data bus anyway, but yeah…

Somebody on Twitter poked me for a problem they have on their Oric 1, apparently when Erebus is connected there's just garbage on the screen.
Any idea of what that could be? (It's a 48k Oric 1, and apparently the power regulator was replaced by the Trapco model).

See:

There are two possibilities:

1: The assembly needs a 900mA power supply, the switching regulator may be too light.
2: The Oric uses a 27C128 UVPROM instead of the original ROM, the ROMDIS pin is not functional. Some UVPROM chips are compatible.

Thanks, transmitted the information

For the checking, the RomBasic chip inside the Oric computer can be removed while using the Erebus interface.

I removed the ROM and still not able to boot. But when I had the rom in, and repeatedly pressing the reset on the EREBUS, I did managed to boot once or twice and it crashed shortly afterward, and when I press reset again the ram reported started disappearing. Could this be dram issue? (I know these 4164 is not very good and most of the fails on the Apple II).

thanks,
eddie

Hello
Try it with an LM7905 regulator.
What are the characteristics of your power supply unit ?

hi,
I am using a new LM7905 regulator. I am using 9V standard adapter (don't have an original oric power supply). I also tried my bench power supply as well.

thanks,
eddie

hi all,
After testing some more I am sure its the power supply I am using causing the issue. I will get another power supply / cable+plug. Looks like the Oric is very sensitive to power.

thanks,
eddie