A SURVEY OF CP/M ON SHARP COMPUTERS
written by Maurice Hawes / SUC/UK
Source: SUC-magazine March 1993, Volume 13 Number 1, p. 13 - 16
|Sharp Users Club - CP/M Section - Survey of CP/M on Sharps|
The CP/M system was invented by Dr. Gary Kildall. It was intended for Intel 8080-based machines; but as it happened, it also suited the more powerful and popular Zilog Z80 CPU, and this eventual settled to CP/Ms success. In a nutshell, CP/M is a software interface between programs and hardware, which makes all Z80 hardware look' the same; or at least, as nearly the same as can be managed.
CP/M demands a machine with disk drives and at least 20K of RAM ( which
must start at $0000 ). And although there is no theoretical lower limit
on VDU width, less than 64 columns is impracticable. Some of Sharps
Z80-based machines meet all the criteria, but some do not. Given their
divergent designs, one cannot generalise; so I now turn to the individual
machines, in chronological order.
|MZ-80K ( 1979 )|
Crystal Research of Torquay devised a fix for the ROM problem and wrote a 46K CP/M system for the MZ-80K which, initially, was designed for the MZ-80Ks 40-column screen. But the package never really took off; this was probably due to the unhelpful attitude of Digital Research, the limited capacity of the MZ-80Ks 35-track 5.25" disks ( 143K ), and difficulties in upgrading the 40-column screen, rather than any deficiencies in Crystals CP/M software.
The Sharp Users Club has done a lot of work in an attempt resuscitate the idea of CP/M on the MZ-80K, but we have recent concluded that the problems are almost insurmountable.
This does not mean that the K is no use. Other K DOS systems ( e.g. Brian Gladmans SDOS and ZEN DOS ) offer facilities similar to CP/M without demanding expensive and difficult hardware modifications and they turn a disk-based K into a useful software platform.
Note by the author of this site: My MZ-80K is able ( by hardware modifications ) to run CP/M Crystal Electronics version 2.21 40-columns ( 46K ), CP/M Crystal Electronics version 2.23 80-columns and its modified version for 80 tracks ( both 48K ).
|MZ-80B ( 1980 )|
Although it appeared only a year after the MZ-80K, the MZ-80B is very different, especially in the context of CP/M. As manufactured it has a switchable 40 / 80-column screen, 64K of RAM, and 35-track 5.25" disk drives with a capacity around 300K. Therefore it does not have to be modified in any way, to run CP/M.
Nevertheless, it appears that Sharp did not see the MZ-80B as a business machine; at any rate, they didnt produce a CP/M system for it. The job was left to MicroTechnology Ltd.; and a very good job they did, too. They not only produced a reliable and friendly system, they also increased the capacity per disk, from Sharps original figure of 286K, to 350K ( and that was done using Sharps 35-track drives - on 40-track drives it would have been 400K ).
As a result, the MZ-80B was accepted as a business machine, and MicroTechnology
went on to produce a hard disk system which gained many customers. They
also implemented CP/M PLUS on the MZ-80B; but this was overtaken by
events, and was never properly debugged.
|PC-3201 ( 1980 )|
The proper solution to the problem came from MicroTechnology; they designed a Relocator Board which plugs into one of the I/O slots at the rear of the PC-3201. The BASIC-in-ROM chips are then removed from the main PCB and plugged into the Relocator Board, after which they are automatically switched out of the main 64K area whenever the user loads the M-T version of PC-3201 CP/M.
M-Ts version looks and feels identical to their MZ-80B
CP/M; so anyone used to M-T CP/M will feel at home on either machine.
But for some reason the two systems use different disk formats - 350K
/ disk on the MZ-80B, but only 256K / disk on the PC-3201. As it happens,
this is not a serious problem today; MicroTechnologys CP/M system
for the later Sharp MZ-3500 can handle both of these ( and some other
) foreign disk formats.
|MZ-80A ( 1981 )|
We can legally supply our members with Kumas MZ-80A 80-column
kit. We also offer an enhanced version which allows you to restore the
MZ-80A to its original 40-column MZ-80A / MZ-80K configuration.
|MZ-3500 ( 1982 )|
|MZ-700 ( 1983 )|
Tim Cowell, a member of the Sharp Users Club, and the Sub-editor of the MZ-700 section in 1985 - 1988, designed a plug-in module which solved the problem by utilising the Z80s external ports; Peterson Electronics showed considerable initial interest in this device, but for some reason they did not follow it up. Sharpsoft and Kuma also announced 80-column kits ( possibly the same kit in each case ), but nothing concrete ever seems to have appeared.
In 1989 the SUC took the first step towards a full-scale CP/M for the MZ-700, when member Dave Bagshaw modified the 48K MZ-80A version of CP/M to form a 52K system on the MZ-700, albeit in 40-columns only. This was a good start, enabling us to offer MZ-700 owners a disk version of our ever-popular WDPRO Word Processor.
Then, in 1990, John Edwards devised a very ingenious 80-column modification, involving a small additional PCB with flying leads and a few alterations to the main PCB. The SUC can supply the mod., in kit form for around £15 ( to members only ); once this is fitted, the MZ-700 screen may be switched into 80 columns.
Shortly afterwards John wrote a CP/M patch ( CPM780.COM ) which modifies Dave Bagshaws 40-column CP/M to suit the 80-column hardware. In essence, the MZ-700 can now run almost any standard CP/M software; but to take full advantage of the 80-column screen you really do need a proper computer VDU, rather than a TV set.
The story does not end there. As reported in the 700 section of this
issue, we now have an MZ-700 version of the 64K PCP/M system that Sharp
marketed with MZ-800. By the time this issue appears, anyone who uses
an 80-column MZ-700 with 40-track drives will be able to choose between
TWO different CP/M Systems - one based on M-Ts MZ-80A CP/M, and
the other based on Sharps MZ-800 PCP/M. The PCP/M disk format
is 40-track, 320K ( but with some odd-ball features, see Vol.12 No.1
p.60 ); but PCP/M has a DISKDEF utility which allows Drive B: to read
other Sharp-CP/M 35 / 40-track formats ( MZ-80B, MZ-3500, MZ-5500 );
so there is good inherent flexibility.
|MZ-800 ( 1984 )|
|COMPATIBILITY and PROGRAM TRANSFER|
There are points to watch. M-Ts various CP/Ms do not all
use the same disk format, and PCP/Ms disk format is different
again. Having said that, there is no problem transferring CP/M software
between machines. The key is in M-T CP/M on the MZ-3500;
this can read / write M-T CP/M disks from the PC-3201 and MZ-80B / A
/ 700; and its own disks can be read / written by PCP/M.
|DIFFERENCES IN SYSTEM FILES|
Format disk B, when ready type return to start
all on one line; but MZ-80A FORMAT.COM prints the same message on two lines. Having discovered this, I compared the corresponding CP/M systems files on the MZ-80B and the MZ-80A. The results were:
PIP, SUBMIT, XSUB, ED, ASM, DDT, LOAD, STAT and DUMP, SYSGEN, DEL, EJECT, and BUGFIX are all absolutely identical.
MOVCPM, BACKUP, CMT, CONSOLE, CONFIG, COPY, FILES, FORMAT, IODEFS, and TIME are different.
In the next issue, I shall discuss the individual files in M-Ts
various versions of CP/M, and in PCP/M, including those files which
M-T or Sharp added to the standard Digital Research list.
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