Modifying PCP/M for use with older Sharp disk drives
written by Maurice Hawes / SUC/UK
Source: SUC-magazine July 2003, Volume 23 Number 2, p. 16
The Sharp/Digital Research version of PCP/M for the MZ-800 was meant to be used with the new Sharp 5.25″ FDD units that appeared on the U.K. market at the same time as the MZ-800. These units ( 1-drive MZ-1F19, 2-drive MZ-1F02 ) can be stepped at 6mS, which is much faster than the stepping rate of 30mS used with the old MZ-80FB drives fitted to the MZ-80K, MZ-80B, and MZ-80A.
STEPPING RATE PROBLEMS WITH THE MZ-800 PCP/M SYSTEM AS A WHOLE
As supplied, an original MZ-800 PCP/M master disk carries a PCP/M system that is set up for a disk stepping rate of 6mS, and in order to boot and run the various system files, the MZ-800 must be fitted with Sharp MZ-1F01 or MZ-1F19 disk drives ( or an equivalent drive unit such as EPSON TF-16 ).
However, once you have booted MZ-800 PCP/M, SETUP.COM allows you to reset the disk stepping rate to 12mS, 20mS or 30mS and save the new setting on the current master disk. In this way you can create a master disk with the disk stepping rate set to 30mS; this disk will boot in an MZ-80FB disk drive, and most of the programs on the disk will work correctly.
SPECIAL PROBLEM WITH MZ-800 PCP/M FORMAT.COM
However, there is a special problem with the 40-track FORMAT.COM utility supplied with MZ-800 PCP/M. This ignores the ‘system’ disk drive routines, and uses its own low-level disk routines and a stepping rate of 6mS. As a result, if you try to use this program to format a disk in an old MZ-80FB drive, it falls at the final hurdle with a ‘disk error’.
The result is not catastrophic, because the disk has in fact been formatted correctly and the only thing wrong with it is that it does not contain the boot track or the PCP/M system. Therefore it may still be used as a non-system disk for data files, or as a ‘Target’ disk for creating a brand new master disk by using a whole-disk copying program such as COPYDISK.COM.
‘FORMAT.COM’ v.2003 ( FOR OLD SHARP 5.25″ DISK DRIVES )
Our own MZ-700 versions of PCP/M ( created by Robin Hill in Australia and developed by the SUC in the U.K ) suffered similar problems in their early days; but by 1993 we had a set of master disks with the disk stepping rate preset to 30mS and, thanks to John Edwards, a revised FORMAT.COM that works with Sharp MZ-80FB drives. Until now, this revised MZ-700 version of FORMAT.COM has never been mentioned in these pages; this oversight is entirely my own fault, and in a belated attempt to compensate for it I have recently produced a similar MZ-800 version and ‘tweaked’ their opening messages to make them instantly recognizable – they now display the legend ‘FORMAT v.2003’.
To run PCP/M on the MZ-800 or MZ-700 with the older type of Sharp MZ-80FB 5.25″ disk drives, you need a system disk with the disk drive step rate preset to 30mS, and the ‘2003’ version of the program PCP/M FORMAT.COM ( which formats a 5.25″ disk to 40 tracks and then adds the boot track and the PCP/M system file ).
There are NO SUCH RESTRICTIONS if you are using more modern 5.25″ disk drives such as Sharp MZ-1F02 or 1F19, or Epson TF-16; or if you are using 3.5″ drives to operate one of the 3.5″ 80-track PCP/M systems mentioned on the following pages.