From: David Wood (
Date: 2004-09-09 15:08:47

0 means 256 bytes, I remember reading this somewhere.  It probably has
something to do with the way the countdown loop is run: dex:bne would cause
0 to be 256 bytes, 1 to be 1, 255 to be 255.


On Thu, 9 Sep 2004, Marko [iso-8859-1] Mäkelä wrote:

> Hi Ruud,
> > > Hmm, if you were copying individual files, wouldn't it be
> > > possible to tell the CBM-HD to LISTEN and the 8250 to TALK?
> >
> > You mean sending a TALK to the 8250 and a LISTEN to CBM-HD? On itself a good
> > idea as there is only one transfer par byte instead of two as it is now.
> > Transferring files isn't a problem as the sender will activate EOI at the
> > end of the file. But how are you going to tell the sender to activate EOI at
> > the 256th byte?
> I didn't think that it would be a solution for disk transfers; I just mentioned
> it as a compatibility test case for your CBM-HD.
> Come to think of it, it might work also for disk image transfers.  You'd write
> a program for the 8050 or 8250 and start it with M-E.  The program would wait
> for the LISTEN or TALK request, and then it would start transfering disk
> sector data.  The CBM-HD would receive all data in a single file.  Copying
> back to disk wouldn't work as easily.
> > But the docs state that one can only read from 1 up to 255 bytes. I need to
> > read 256. I could try if 0 is translated as 256 otherwise I have to do it in
> > two batches.
> cbmlink uses M-R length 0 and copies 256 bytes at a time.  I don't remember
> if 0 means "infinite"; you will have to test it.
> > More worrying is the fact that I only can write up to 34 byte. Is the
> > computer to blame or the drive?
> The drive.  It has a fixed-size command buffer.  It'll input the data to the
> buffer, and then copy it to the desired location.  M-R reads directly from
> the specified address.
> What language is CBM-HD written in?  Are you planning to release the source
> code?  I'd be interested in a GNU/Linux port.  I have an old IEEE-488 ISA card
> lying around.  I hope that the code is modular enough to support different
> types of IEEE-488 interfaces.
> 	Marko
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