Re: CBM900 hard disk timeout

From: Michał Pleban <>
Date: Sun, 24 Aug 2014 21:34:51 +0200
Message-ID: <>

Martin Hoffmann-Vetter wrote:

> This is a good question. It's possible the INDEX line isn't used.

I checked on the controller PCB that the line goes to some TTL chip so I
guess it might be used by the controller. Maybe there is something wrong
with my drive, or maybe indeed it does not send this signal as it
should. I am waiting for the new drive PCB from MikeS which might solve
this problem.

> I think the problem must be the readed data. So there are two case, first the disk isn't formatted, or there are problems zu transfer und decode the data from the disk to the memory. Did the c900 read the data via dma?

All transfers to the controller are via DMA. The computer lays a
six-byte command block in memory, then instructs the DMA chip to send it
to the controller, and read the status and data.

So it's also possible that the 8716 DMA chip is broken in some way. That
would be most unfortunate as there is no possible source of this chip
other than another C900. However, I believe that the same chip is used
also to send commands to the floppy, and the floppy works fine (the
schematic is a bit unclear to me on this point, but the documentation of
the floppy controller does mention that the data goes through the 8716).
So hopefully the chip is working.


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Received on 2014-08-24 20:00:02

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