Experiments with 3.5" & 5.25" MZ-700 Disk Basics
written by John Edwards / SUC/UK
Source: SUC-magazine November 1989, Volume 9, Number 3, pp. 60 - 61
But the modern floppy disk controller chip on the 3.5 disk card is very flexible indeed, and by sending it the correct parameters, it is possible to make it read and write a very wide variety of disk formats. As Maurice and I discovered very soon after we were sent the drives June 1989, the F.D. card could be connected to standard Sharp 5.25 floppy drives with only one simple wiring modification, and would then boot the 5.25 K&P Disk Basic V1.04KP'. Since then I have done some more experiments. The first one was to try booting the Sharp 5.25 Disk Basic, 2Z-009E on the same system. This did not work. When I investigated the problem, I found that this was because K&P and Sharp disk Basics on the MZ-700 are loaded in fundamentally different ways.
The K&P F.D. eprom loads the K&P file ( size $8800 ) at $1200, and then immediately executes it at $9229; there, a short routine in RAM switches out the Monitor ROM, copies the whole file down to $0000 and then executes a cold start by jumping to $0000. The IPL sector of track 0 on a K&P 5.25 master disk is as follows:-
Sharps DBasic 2Z-009E system does things differently. The Eprom on the F.D. card loads the Sharp file ( size $9000 ) at $1200; but it also switches out the ROM Monitor and copies the code down from $1200 to $0000. Only then does it release control to RAM, by jumping to the code now at $0000. The load and execute addresses of this DBasic appear as $0000 on the IPL sector on sector 1 of track 0, so to the uninitiated it looks as if they are missing:-
Once I realized this, I made a copy of the 2Z-009E Master disk and patched the Sharp Disk Basic file, starting at $85B0, with a loading routine similar to that used in the 2Z-009E F.D. eprom ( note by sharpmz.org: the EPROM from MZ-1E05 ). Then I changed the IPL sector of the disk ( 1st byte to 02 so that a K&P-type Eprom would load it, LOAD address to $1200, and EXECUTE address to $97B0 ). This modified Master disk booted up via Alan Waites 3.5 F.D. card. And, of course, it also booted up via the K&P section of the composite SUC F.D. Eprom on a modified MZ-80A F.D. card ( as used by several members of the Club ).
The added loading routine in 2Z-009E ( at $85B0 in the file, but at $97B0 when it is in memory ) is as follows:-
LD A,FF CP FF OUT (E0H),A ;switch out Monitor ROM LD HL,1200H LD DE,0000H LD BC,85B0H LDIR ;copy Monitor + Interpreter ;down to $0000 LD BC,0200H ;instruction as in 2Z-009E eprom, ;use not clear LD HL,0000H JP (HL) ;jump to cold start
At this stage I noticed an advert by the Morgan Computer company in London, offering a Sharp 3.5 double-sided 80-track drive for £35 plus VAT. After consultations, Maurice and John Duxbury agreed that the Club ought to buy one for tests, to see if it could be substituted for 5.25 drives. I daisychained the drive with a standard 5.25 drive, on an MZ-80A card fitted with a K&P Eprom, and was able to copy both the above disk Basics ( i.e. K&P V1.04KP, and Sharp 2Z-009E with my loader ) to the 80-track 3.5 drive, and reboot them there. I used the K&P 5.25 software to format only half the surface of the 3.5 disks with 40 tracks, and to do the copying. The disks will also boot off the Sharpsoft 3.5 card.
So it begins to look as if we can all modernize our MZ-700 disk systems to 3.5 if we wish; a comforting thought for the future. I aim to do further experiments, to see if I can double-step the 3.5 80-track drives, to produce conventional 40-track disks.
There is one major hurdle still to be overcome. Many programs, including most of the utilities supplied with the different disk Basics, look for particular routines in the area above $F000, expecting them to be supplied by the F.D. Eprom on the I/F card. The Sharpsoft 3.5 sds eprom contains the required K&P routines in the right places; but it does NOT contain the Sharp 2Z-009E routines. Therefore the utilities supplied with K&P DBasic V1.04 work with the Sharpsoft 3.5 card, but those supplied with Sharp 2Z-009E DBasic do not. It would be a major advance if we could get the 2Z-009E utilities working, as they are so much more powerful than the K&P versions ( which are merely tarted-up versions of the old Sharp utility programs on the MZ-80A and MZ-80B ). This is not an urgent matter, as the K&P utilities will copy Sharp 2Z-009E onto a 3.5 disk. However, it is something I intend to work on.
Finally, a word about the sds utilities which come with the Sharpsoft 40-track single-sided 3.5 drives. These clearly stem from the earlier Sharp / K&P utilities, but they are significantly different as they contain new routines to send vital parameters to the more up-to-date controller chip on the Sharpsoft disk card. Not surprisingly these routines resemble the routines used in the eprom-based Minidos on the same card, which is discussed in more detail on the next pages. The difference is that the routines in the sds utilities are preprogrammed to give 40-track 18-sector single-sided disks; whereas in the Minidos the routines require keyboard input to set the parameters.