HP 9816 CP/M-68K

js at cimmeri.com js at cimmeri.com
Mon Feb 12 16:56:55 CST 2018

On 2/12/2018 3:52 PM, Glen Slick via cctalk wrote:
> On Mon, Feb 12, 2018 at 12:34 PM, Eric Smith via cctalk
> <cctalk at classiccmp.org>  wrote:
>> Format a track with the sector size that occurs later on the track, with
>> dummy sectors ahead of them and gap sizes selected to position them
>> properly.
>> Start formatting with the sector size for the earlier sectors. Abort the
>> format at the time when the desired number of sectors have been written.
>> I'm not sure whether there's any way to abort a track format on a PC. I did
>> it on a machine that had control over the μPD765 reset pin.
> Bit 2 of the Digital-Output Register at 0x3F2 resets the FDC when the
> bit is clear.
> I used that on my 5150 back in the day when I bought it new to
> reproduce a copy protected disk that used sectors with bad CRCs as one
> of its protection mechanisms. Feed the sector data a byte at a time to
> the FDC in PIO mode so that the timing is controlled, then toggle the
> FDC reset bit in the DOR just at the time when the CRC is being
> written.

That's really "slick," Glen.    If it's not too burdensome to give a 
brief answer, how would you keep track of the time, or know how long 
feeding a byte at a time took?

- John

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