"I have been using a Commodore Pet Computer now for some time together with a 3040 Floppy Disk Unit and was wondering whether you or one of your associates, e.g. Jim Butterfield, can answer a few questions for me. alternatively, a source of such information would be useful.
My questions concern the Disk Drive for which Commodore appears to publish very little other than the Handbook.
I think a Manual which gave some (if not all!) of the subroutines would be a useful item.
The point of most interest to me concerns the individual blocks on a formatted disk. It is possible to change the ID on a particular track & sector to be different to the main ID shown in the directory ? How can one go about this? Once changed, can this be altered back again"?
My other point concerns the ‘U’ commands. We know from the manual that ‘U1’ will ‘READ’ & ‘U2’ will ‘WRITE,’ but what other commands are there involving ‘U’ and what do they do which is useful. Are the routines available only by MACHINE-CODE access?
May I say I find COMPUTE! the best magazine of its kind on the market, but I have great dificulty in obtaining it. I would be grateful if you would tell me if it is directly obtainable from you on a regular basis, or where the best source in London would be.
I hope you do not find my questions impertinent — they are not intended to be." M. J. Band
COMPUTE! expects to publish a program shortly which will permit easy viewing and changing of any byte on a disk including the directory, BAM, etc.). In reference to your question about the "U" commands, they are "user-defined" and described briefly on page 53 of Commodore's User's Manual for CBM Dual Drive Floppys (Part Number 320899).
Thanks for the compliment. COMPUTE! subscriptions are available from: Circulation Department, COMPUTE! Magazine, P.O. Box 5406, Greensboro, NC 27403 USA. The cost is $25 surface mail anywhere in the world, $38 airmail to Europe.