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   Message 3 of 190
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   Re: C128D  more options
   
   
   Author:   Nicolas Welte
   Email: welte@chemie.uni-konstanz.de
   Date: 1998/12/28
   Forums: comp.sys.cbm
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Cameron Kaiser wrote:
> I tried setting REVCNT to 0 on the drive (M-W to 106). The drive chewed over
> and over and over on the disks it didn't like, and behaved normally with the
> ones it favoured. Finally it gave up and hung the serial bus. Storing 255 to
> REVCNT caused it to hang the bus immediately on any disk.

106 is the memory location I mentioned in my last message, it does not
only control the number of retries, but is also responsible for
controlling the head bump on retry and the retry on halftrack feature.
If bit 7 is 1, bump is disabled, if bit 6 is 1, the halftrack feature is
disabled. Bits 5-0 hold the number of retries value, so 63 is the
maximum number you can store there. Note that this is the number of
retries per track, which means the total number will increase if the
halftrack and bump feature is enabled. I'm not sure which effect the
number zero has in this location, it is either 0 retries or 64 retries,
but I don't want to try it now.

> Sending a u0>ra causes the drive to behave normally. I forget what this
> command does exactly.

I'm not sure, but I always thought this command only writes the
specified value into memory location 106, and therefore also controls
the number of retries and the other two features. An "a" is ASCII 65 and
therefore sets number of retries to 1 and disables the halftrack
feature. Should make the detection of single sided disks a lot faster.
Or did you mean CTRL-A, which would be ASCII 1?

> On a somewhat related note, what was the command to flip drive heads? I thoug
ht
> it was u0>h1 but the v3.0 and v3.1 drives both complain with error 31.

You can only select heads when you're in single sided (i.e. u0>m0) mode.
In native mode, this gives an error as you already know ;-)

Nicolas
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