UNOFFICIAL TECHNICAL MANUAL
AND FURTHUR INFORMATION
FOR THE FD-ZX FLOPPY DISK INTERFACE
THE ZX81 AERCO DISK SYSTEM
WITH HELP FROM THE FOLLOWING:
RICHARD MATEJOVIC
FRED STERN
FRANK DAVIS
JERRY OF AERCO
THIS IS A PUBLIC DOMAIN PUBLICATION. FEEL FREE TO COPY AND OR PASS ON REALIZING THAT NO ONE ACCEPTS RESPONSIBILITY FOR ANY DAMAGE TO HARDWARE OR SOFTEWARE RESULTING FROM USE OF INFORMATION PRESENTED HERE.
This publication is dedicated to the FD-ZX Floppy Disk users. This is to be a source of information for the FD-ZX users. If you know of anyone using the ZX81 and the AERCO disk interface please let them know of this publication and/or let me know of them by supplying me with their mailing address.
For those still using the ZX81 (MicroAce, ZX80 with 4K ROM, ZX80 with 8K ROM, the ZX81 and the T/S 1000 and possibly the T/S 1500 (I do not believe the PC8300 will work since the hardware is different) AERCO is still manufacturing them along with anything else they have manufactured for the T/S computers. I believe that the price is around $179.00 but am not sure. That is just for the interface, BOOT disk and necessary cables, the disk drives, case and power supply are extra. The on board EPROM for the disk controller has to be programmed for the disk drives you will use. Also, the disk drives have to have a minor alteration done to get the +5 and +12 volts supply to the disk controller board. The interface will handle any Shugart standard drive but you have to have all drives the same speed and the same track access time. The drive sizes run from 3 inch to 8 inch (single denisty only on the 8 inch) and the speed from 6 to 30 msec and the tracks 35/40/80. I am not absolutely sure that single sided and double sided disks can be used together. It is best to call them for furthur information. The address and a working telephone number as of 02 28 1991 is:
AERCO (ACME ELECTRIC ROBOT CO); BOX 18093; AUSTIN, TX 78760; TELE: (512) 451-5874.
The FD-ZX EPROM normally occupies the region from 12K (12288) decimal to 14K (14336) decimal (3000 to 3800 HEX) but can be ordered special to put it in another location which may require a change on the board. The special EPROM can be at (8/10/14K) but then the all USR calls must be changed accordingly. (*** I wonder if more than one EPROM could occupy the board so that different disk drives could be used? ***) If you are using 64K the particular area of the 8 to 16K that the EPROM uses will have to be switched out.
The T/S 2040 printer may cause problems with its electronic noise.
The DOS occupies 8K so a minumum of 16k RAM has to be installed to use the system BOOT disk. (*** Can one fly blind and use USR calls to SAVE and LOAD so that more than 8K can be in a program with only 16K ram added? ***)
I bought my sytem sight unseen from a person in California. He was reluctant to ship since he could not get the BOOT disk to LOAD. I agreen to accept it as is. I also had problems with the BOOT disk only since I had the drive case open I could see the worm on the disk track mechanism and it seemed to be slow or jerky. So I put in a blank disk and ran it a while with the RAND USR 13303 till it seemed more perky and then it would LOAD the BOOT disk. After a little playing with the sytem I went to the SMUG FEST and not long after that we were involved in buying a house and packing to more and just a few days ago I got the old AERCO system out and started to play with it again. I did note that the storage space on the disk was small but so it is with the Larken ZX81 system. That and not being able to name the file at the time of SAVE like on other systems did turn me off originally. And my system has a single sided disk drive only. But recently I tried to SAVE a program on the Larken system and it would not SAVE and I learned that I had to POKE in the starting address and the length of the machine code to SAVE a program with machine code. And two FD-ZX disk drives are in the local users group plus there is another user in LISTing. So it was with renewed interest that I got back to the FD-ZX floppy system.
But the disk drive on my system bugged me, and then I got a more recent copy of a FD-ZX manual and lo and behold I saw that with my system the maximum number of pages with a single sided drive is 8 and 16 with a double sided drive and with the new manual it gives 10 for single sided and 20 for double sided drives – but the manual also calls out the 8 pages as maximum for 35 track single sided and 16 for double sided 35 track and 10 for single sided 40 track and 20 for double sided 40 track. And in my manual and the newer manual the USR calls for 35 track 8 pages and 16 pages are the same. One mystery solved, I have a 35 track single sided drive. My manual also referenced to 8 inch drives which are single density and from casual conversation I believe are 35 track drives. So I will need an EPROM to be able to change over to 40 track drives. And possible a new BOOT disk, I suspect that if I SAVEd the BOOT program to cassette and reLOADed after I have the 40 track EPROM then I would have it. Be easier with a BOOT disk in 40 track though. As I wrote before it could be done with USR calls but you could not read the directory so you would be working blind.
I have heard of someone that has wrote a routine to name the directory as you SAVEd the page. I will try to get a copy of that program.
Unlike the Larken, SADDOS will SAVE machine code with no pokes. That would be better than Larken and besides 20 pages on a disk over 16 is much better, or should I say 19 since one is the BOOT program.