Cumana Disk Interface Logic

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Vyper68
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Cumana Disk Interface Logic

Post by Vyper68 »

I have been trying to get my self-built Cumana interface to work on and off for a couple of years now without success. I have tested all the LS Logic IC’s and bought new FDC’s and burned new ROM’s without any success. The PCB tracks all go where they should, no shorts or breaks. So I am baffled really.
I was testing my friends Microdisc early this year as his 3” drive was out of alignment and I connected a Gotek to his Microdisk PCB and booted Sedoric right away. That kind of rules out a problem with both my Oric’s in general, I was wondering if there would be any benefit to replacing the 74LS Logic on my Cumana with 74F where available for exampleas the 74LS244 replaced with 74F244? I know some cannot be as I cannot source some alternative fast versions.
I am just thinking out loud here really and wanted to hear if anyone else has changed the logic on their disk interface to the faster version.
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Dbug
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Re: Cumana Disk Interface Logic

Post by Dbug »

What happens when you connect your self-built board?

Normally, the Cumana behaves like the Oric one, and before it even accesses the FDC it takes over the Oric ROM by running its own eprom.

What about replacing the Eprom by something that for example changes the screen color to RED and prints a message, to know at least if your ROMDIS/MAP handling is working?

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Re: Cumana Disk Interface Logic

Post by Vyper68 »

Hi Dbug,
I get the “Insert System Disk” message on the screen, sometimes I get a activity light on the Gotek but nothing is loaded. The Gotek is running the HxC firmware, I do have another with Flash Floppy and it does the same. I have tried different Floppy cables and cables connecting to the Oric so it’s not cables. Given my Oric’s worked with the Microdisk and The same Gotek the problem is there somewhere.
Can you point me to this ROM you talk about please.
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Re: Cumana Disk Interface Logic

Post by Chema »

If you get the "insert system disk" message, chances are that the Eprom is kicking in correctly. There could still be a problem with the timing of the MAP signal, if it is not able to boot (I have seen this, as strange as may sound, as the Eprom seems to work). If you have a variable resistor somewhere to adjust it, maybe you could give it a try, but I guess you have already done so.

I am suspicious because you say that only "sometimes" the disk access light comes in... The usual behaviour with a real floppy drive is turning on the led and keep it lit even with no disk inserted (if I recall correctly). As soon as you put a disk, you hear the usual access noise.

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Re: Cumana Disk Interface Logic

Post by Vyper68 »

I have a 3.5” Drive and some 3.5” Disks but no means of putting Sedoric on a real 3.5” disk to test it.
I have adjusted the 2.2K Variable resistor several times and it seems to be in the best setting to give the boot screen.
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Re: Cumana Disk Interface Logic

Post by iss »

One easy thing to try: if you have working Microdisc interface then you can use Microdisc's EPROM with the Cumana interface and FF/HxC floppy emulator.

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Re: Cumana Disk Interface Logic

Post by Vyper68 »

iss wrote:
Mon Aug 02, 2021 12:40 pm
One easy thing to try: if you have working Microdisc interface then you can use Microdisc's EPROM with the Cumana interface and FF/HxC floppy emulator.
It has gone back to my friend now so I don’t have access to any other disk drives. I do have a secondary Cumana PCB that I planned to power with 5v DC direct and bypass the 7905 regulator and capacitors that feed power into the Oric and power both separately but I haven’t got round to it yet.
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Re: Cumana Disk Interface Logic

Post by Steve M »

Hi,

Sorry, I haven't had time to sort things out for you. I have a board that I know works which doesn't boot with the extra power supply for the drive(s).

I keep meaning to sort a different power supply to test it works properly -then I can send it to you to compare. Currently it does something similar to yours and won't boot the disk. The interface was working fine in a different case so it has to be the drive power supply (in my one).
Orics seem fussy about power supply. I remember Jon H having issues with his system at the OUM meets. (It worked OK at his home.)

The connections can be a bit confusing. I managed to get a ribbon cable the wrong way round, which knackers things. The cable was made right but I plugged the wrong end in the Atmos. I've been told that shouldn't matter as pin 1 connects to pin 1 etc- but it does. If you have a working system it's a bit easier to compare to make sure things are in the right places.

I've a lot waiting to sort out and need to find a good box to fill. Sorry. I don't get into the Oric room much. There's so much that needs sorting it can be a bit overwhelming.
I'll endeavour to try and get a look at the hardware now I've sorted most of the scanning.

Steve M

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Re: Cumana Disk Interface Logic

Post by Vyper68 »

Thanks Steve, I am going to get another PSU and keep trying. I bought one of the new Omniflop Gotek PCB’s to try so will keep on tinkering.
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