ZX81 floppy disk systems

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David G
Posts: 318
Joined: Thu Jul 17, 2014 7:58 am
Location: 21 North, 156 West

REVIEW: Aerco FD-ZX (TS Horizons April 1986)

Post by David G »

In this review:
  • the Aerco board came with a Siemens FDC 1797 instead of the SMC version in the last review
  • Rather than USR commands only as in the last review, he explains the menu-driven SADOS+
The existing DOS control software simply doesn't take advantage of the FD-ZX hardware's potential ... the incredible speed of reliable access to a large number of programs or files makes it easy to overlook the shortcomings of the DOS.
From T-S Horizons No. 18 (April 1986) pages 18-21
ZX 81 NEWS AND RESOURCES by Peter McMullin


Subject: Aerco FD-ZX Floppy Disk System
Source: Aerco, 7606 Robalo Rd, Austin TX 78757

FD-ZX Floppy Disk Controller Board and DOS: $179.00
Auto Boot ROM Board: $ 59.00
Auto Boot ROM Board with Centronics I/F: $99.00

Complete packages are also available.

NOTE: See "Bug Alert", last issue for a discussion of the Boot ROM/Centronics board.


Drive type: Shugart compatible 3", 5" or 8" drives, 1 or 2 side, SD or DD, 35 or 40 tracks per side.
# of drives: up to 4.
DS/DD Capacity: 400K bytes.
Disk Format: IBM readable, 10 sectors per track, 512 bytes per sector.
#Files per disk: up to 20 (as 4-track pages) up to 6 (as 12-track pages)
Memory use: 2K DOS in EPROM, and FDC at 12-14K
FDC I/O is memory- mapped.
Format DSDD: approx. 35 seconds.
Copy DSDD-DSDD: approx. 1 minute, 5 seconds.
Avg. LOAD/SAVE: 3 sec. (20K page) 5 sec. (60K page)
Physical size: Circuit board is approx. 4.5 x 6", gold finger extensions.
Special ICs: 1797 FDC (Siemens): 9216 Data separator.

What do you see when you open the box containing your newly arrived AERCO FD-ZX? One uncased controller board, a computer bus ribbon cable, one floppy disk, and a 16 page manual. What else do you need? Disk drive(s), drive cables, cases and power supply. Aerco's manual gives reasonably easy- to-follow instructions for hooking up your system, and has several useful illustrations. The power supply must provide +12V at 2-3 amps and +5 at 3 amps. The drive cable required is a standard IBM/ Shugart 34 conductor pc-edge type. If you follow Aerco's instructions to the letter, you will likely void any warrentee on your new drives. The FDC board gets its +5V and +12V supplies via pins 2 and 34 on the disk drive edge connector. Pin 34 is normally unused, but pin 2 is connected on some drives. Aerco recommends you cut any traces going to pins 2 or 34 on the drive and jumper these over to the power supply pins. This way you connect the power supply only to one drive, and the FDC board and other drives get powered through the ribbon cable. The result is tidy but I hate to hack up a new drive! The alternative would be to cut wires 2 and 34 adjacent to the contoller card, and run separate power leads to everything. I did it Aerco's way.

Having hooked up drives and power supply, the FD-ZX plugs into the supplied ribbon cable; then the RAM pack, etc. onto the ribbon cable's male edge extender, and we're ready to see what's on Aerco's ‘master" disk.

On application of power, the K cursor appears. Following Aerco's instructions, the master disk is placed in drive A. The command RAND USR 13303 initialises the DOS, and loads "page 1" from the disk. The following menu appears on the screen in about 3 seconds:

Code: Select all


Nothing too surprising here. Some further explortion of the manual reveals some interesting facts. All DOS functions are accessed via RAND USR commands. The "DOS" program supplied on page 1 of the master disk serves two purposes: 1) It is a "user-friendly interface" (oh cliche, cliche!) to the DOS USR routines, and 2) It contains the Disk Directory.

Two different DOS control programs are supplied: a "16K" version and a "64K" version. (All capacities specified here are for a 40 track, DSDD drive.)

The 16K DOS permits 20 programs or data files to be saved on a disk. The disk is divided into 20 4-track pages. Any program saved occupies one page, regardless of whether it is a 1K program or a full 16K program. Each "16K" disk page will actually hold up to 20K full of data. Thus it is extremely unlikely that you will ever use the full potential storage capacity of the disk. The 64K DOS assigns 6 pages per disk, each page having a capacity of 60K bytes. It is otherwise identical to the 16K DOS program.

The Aerco D0S does not record a filename with each program, nor does it automatically maintain a directory. Programs are loaded and saved by page number. It is the user's responsibility to keep the directory on page 1 updated.

Converting a breakable program to a disk version is quite easy. Aerco uses sequential USR calls for SAVE and LOAD commands: RAND USR (12720 + PAGE) to SAVE a specified page or RAND USR (12290 + PAGE) to LOAD from a specified page. After loading the program from tape, the DOS must be initialised by the command RAND USR 12865. This command initialises the FDC and loads certain DOS parameters into bytes 16507/16508. Thus the lines:

Code: Select all

9910 CLS
9920 RUN
...would be replaced by the lines:

Code: Select all

9900 RAND USR 12865
9905 RAND USR 12722
9910 CLS
9920 RUN
In this example, a GOTO 9900 would save the program to page 2 on the disk, and autorun. When the program is reloaded, It will come up in the same mode (SLOW/FAST) as when it as saved. To save the program on, say, page 6 instead of page 2, line 9905 would read
"RAND USR 12726."

Having saved a program, it must be entered in the directory. So, entering RAND USR 13303 brings up the SADOS menu. Pressing E gets a prompt asking which page you want to name, followed by the entry of the program name. Having done this, you must re-save the updated directory to page 1. This is offered as a Y/N option when you finish making directory entries, or it can be done by pressing the S at the main menu. Now if you hit L at the menu, the directory appears, listing pages 1 through 20 and their contents. Any program may be loaded by entering its page number, or you may copy the directory to your printer.

D, for DISK UTILITIES, provides selection of PROGRAM or DATA mode, of Disk Drive A, B, C, or D; Single or Double Density, and also a Clear Directory command. In Data mode all variables are saved and loaded, without the Basic program. When re-loading data, no test is made for variables space. Variables must already have been dimensioned or declared so there is enough room between VARS and E-LINE for the disk file to load into. With an understanding of these limitations, the Data mode can be very useful. I've successfully programmed a version of WSII.5 which loads and saves data files ONLY; up to 20 16,000 byte text files, each saved with a filename string. The program will sequentially search a disk for any named file, and print an automatically maintained directory. I'm sure that versions of ZX PRO-FILE (or other file handling programs) could be modified to sequentially search a whole disk, if necessary to find a entry.

CPUs and BUS LOADING: I had just gotten a few programs saved to disk, and was marveling at the speed of program access, when I realized I had problems- random load errors galore. Bytes were simply dropping out of programs. Suspecting bus speed/loading problems, I singled out 2 possible culprits: my CPU, and the ribbon cable provided by Aerco. The NEC D760C CPU in my computer is a notoriously substandard Z80 chip, so I replaced it with a new Zilog Z80B. The Z80B is designed for operation at up to 6MHz., thus has lower intrinsic capacitance, and "stiffer" bus drivers than the slower versions. At the same time, I nixed the ribbon cable, and plugged everything into my new JLO 6-slot motherboard. A ribbon cable can have 5-10 times the capacitive crosstalk as a motherboard the same length, so I figured this would help. Not so simple, though. The male edge connector on the FD-ZX is a mirror-image of that needed by the JLO motherboard! Thus, I had to fashion a "side-swapper" adapter to plug everything together. Having done all this, the problems completely disappeared, and the disk system has been 100% reliable ever since. I don't know whether the CPU or the motherboard was the significant factor, but the combination licked the problem.

IN CONCLUSION, the AERCO FD-ZX system has made a "disk convert" out of this ZX81 hobbyist. The hardware is of good quality and is well assembled. The DOS control program is certainly utilitarian, although some resourceful programming can make it do many impressive things. The existing DOS control software simply doesn't take advantage of the FD-ZX hardware's potential. Aerco's documentation is quite thorough, and provides a few clues to accessing more sophisticated DOS commands thru machine code. The incredible speed of reliable access to a large number of programs or files makes it easy to overlook the shortcomings of the DOS.
David G
Posts: 318
Joined: Thu Jul 17, 2014 7:58 am
Location: 21 North, 156 West

Review: BBDOS - Disk Operating System

Post by David G »

At first I thought, by the name connotations, that it was a DOS developed for bulletin board systems. But actually it stands for Bill Bell DOS
Bill Bell, 596 Cherrington Road, Westerville, OH 43081, (614) 882-3883, is offering BBDOS for the TS1000 equipted with the Aerco FD-ZX Disk Interface. BBDOS is a fully automatic, BASIC transparent, disk operating system that locates itself in the 8-16 K region of RAM. It is advertised as being fully compatible with all printer interfaces. $29.95.
full article
SyncWare News Volume 4 Number 1 September-October 1986 page 23
BBDOS: TS1000 Review

BBDOS: A Disk Operating System for the AERCO FD-ZX Interface

Distributed by:
Bill Bell
596 Cherrington Road
Westerville, OH 43081
(614) 882-3883
PRICE: $29.95

ZX81/TS1000 owners who have been using the Aerco FD-ZX Disk Drive Interface owe Jerry Chamkis and his Texas staff a debt of gratitude for providing them with a reliable, high speed, mass storage system. But even as nice as the FD-ZX unit is, its disc operating system (DOS) leaves much to be desired. The machine code part of the DOS stored in an on-board EPROM performs its job well enough, but the BASIC program that drives it is, to be polite, caveman-ish in its approach.

Enter Bill Bell of the Columbus, Ohio area.

Mr. Bell picked up his first AERCO FD-ZX in a computer "junk" store somewhere on the Eastern Seaboard while on a trip there a few years back. He liked the hardware and the firmware, but was disappointed with the BASIC DOS driver. Which led to the question, "What if...".

Mr. Bell is now offering for sale his disk operating system for the AERCO FD-ZX. The system is BBDOS (appropriately for Bill Bell Disk Operating System). This DOS will take your ZX81/TS1000 and FD-ZX Interface and propel them from the pre-Neanderthal era into the 21st century.

BBDOS is fully automatic and BASIC transparent. The only requirement for its use is that there must be memory available and enabled in the 2000-2FFF (hex, 8K-12K decimal) region of the computer memory map. Once the DOS is installed, it is completely immune to BASIC "NEW" and even system reset (pin 21B of the rear edge connector brought low). To install and start the DOS requires only one RAND USR call. After that, all file handling is done by file name or a function code from the DOS directory. This arrangement completely frees the user from the tedious and mundane chore of disk management.

Other features include automatic handling of 16K/64K page intermixing. Easy conversion of programs and data previously stored with SADOS (the AERCO DOS package). Single file and full disk transfers or moves (copy). BBDOS even allows you to copy files from disk to disk with only a single disk drive connected to the FD-ZX. BBDOS also permits the auto-booting of a selected program from disk upon DOS startup. Provisions are made in the DOS to allow 45 functions to be easily initiated by your own BASIC programs (with just a little effort, your MC programs can even do it!-ed.). By special arrangement with Fred Nachbaur, Memotech, and Ray Kingsley, Memotext, Z-Tools, and Hot Z II can be provided on disk already modified to function with BBDOS.

BBDOS supports 1 or 2 drives, single or double sided. It also supports all printer interfaces currently on the market for the ZX81/TS1000.

While the documentation is not exhaustive, it is more than adequate to get you up and running and completely acquainted with all the features of BBDOS. If any problems or questions do arise, this author has first hand knowledge that Mr. Bell is more than willing to take the time to talk or correspond with you until you both are assured your questions have been answered fully.

I would highly recommend the purchase of BBDOS for use with your AERCO FD-ZX interface. It takes a good product and makes it even better.

Reviewed by Jeff Moore
Anyone have this? Or used it in the past?
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