My ST-2900 Computer Systems

I sold my last remaining inventory of ST-2900 boards and components in 2017, but kept three complete systems, which are described on this page. I have named them System 1, System 2, and System 3.


(Click on a picture for a larger version.)


System 1

icon to link to photo of front/left/top of System 1 icon to link to photo of front/right/top of System 1 icon to link to photo of left/top of System 1
System 1 pictures (530-957KB .jpg).

System 1 is a fully configured 3-board (CPU + FDC + RAM-512) ST-2900 system that I built in 1984 and was my main computer for many years, running FLEX and OS-9. It is powered by an Apple II clone switching power supply rated at +5V @ 5A, +12V @ 4A, -12V @ 0.5A, -5V @ 0.5A. It is mounted onto a 1/8" aluminum base plate, but I never made any cover for it, so it eventually accumulated some dust.

It has two 5¼" 360KB floppy disk drives -- a full-height Qume QT-542 and a half-height Qume QT-142. The QT-542 drive was wonderful -- after I configured it for the optimal step rate, it was fast and quiet and reliable, making only a soft swishing sound when seeking, not buzzing like some drives. But it cost me almost C$450. (When I took this system out of storage, I noticed that the QT-142 was disconnected. Was this because it had stopped working? Don't remember.)

I connected a used Cybernex MDL-110 (pp.19-22) CRT terminal (made in Canada) running at 19200 bps to serial port 1. Serial port 2 went to an SPE-1 switch, one port of which connected to a modem, and the other to my SwTPc 6809 system. This allowed both computers to share the one CRT terminal -- a tiny FLEX program running on the ST-2900 copied data in both directions between the two serial ports to make this work.

A Star Micronics Gemini-10X dot matrix printer rounded out the system. I seem to remember it was originally connected to the SwTPc's parallel port, with the SwTPc running software to act as a printer buffer, receiving data from the the second serial port on the ST-2900. But once I had built the CNT-1 buffer board, I probably used it to connect the printer directly to the ST-2900 rather than through the SwTPc, as that had required me to boot FLEX on the SwTPc before I could print from the ST-2900 -- very awkward.

When I added a RAM-512 board to this system in late 1985, it was even better! The RAM-Disk made no noise whatsoever, was much faster than a floppy disk drive, and having a third "drive" minimized swapping floppy disks. It wasn't quite as good as a hard drive, but was the next best thing.

But as sales of my ST-2900 board sets and DMC floppy disk controller cartridges and related software dried up, I had less need to work on software and documentation for them, so used my System 1 less and less. Eventually I got an IBM PC clone computer (a 286 running MS-DOS, and eventually GeoWorks Ensemble), so used my System 1 even less. When I moved in September 1998 I put System 1 into storage, until ...

Restoration

I hadn't powered this system up for over 23 years, so didn't know if it still worked. I decided to use my old restored power supply for initial testing because the old switching power supply in System 1 wasn't tested yet. On 2021-Sep-12 I applied power to the CPU + FDC + RAM-512 board set and ST-MON 2.04 came alive on the CPU board! I ran a brief memory test on the CPU board's DRAM, then manually entered the machine code to test the RAM-512 board. This test ran for 6 hours with no problems.

I then separated the three boards from each other so I could take photos, especially of the RAM-512 board, which is normally partially hidden in the middle of the stack. After I re-connected the three boards, I verified that the second serial port worked at 19200 bps (as it still had the original 1488 and 1489 ICs and capacitors C3, C4, C5, C6).

In April 2023 I sold the QT-542 drive. The new owner had to replace a tantalum capacitor that exploded, and clean the head rails, but now this 40-year-old drive seems to work OK without any other restoration required.

In June 2023 I modified the CPU board by replacing the 1488 (U1) and 1489 (U11) with MAX1488E and MAX1489E chips, and removing capacitors C3, C4, C5, C6, to support faster baud rates. Powering the boards with my new power supply, I tested the second serial port at 115200 bps and verified it was working.

On 2024-Apr-28 I plugged a new NVRAM board into FDC parallel port B, and successfully accessed the NVSRAM-Disk and EEPROM-Disk on it. I haven't yet tested parallel port A, the floppy disk controller, the QT-142, or the switching power supply. Stay tuned for further progress reports.

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System 2

icon to link to photo of System 2 enclosure icon to link to photo of front/top of System 2 in enclosure icon to link to photo of rear/left/top of System 2 in enclosure
System 2 pictures (44-73KB .jpg).

System 2 is a 2-board (CPU + FDC) system that was originally assembled by my brother in May or June 1984 and used by him for about 4 years. He also built the custom sheet metal box (approx. 9" x 10" x 5"). It has an Apple II clone switching power supply that doesn't list any specifications, but am guessing it is similar to the Apple IIe power supplies that were rated at +5V @ 2.5A, +12V @ 1.5A, -12V @ 250mA, -5V @ 250mA.

The 3½" floppy disk drive is a single-sided 360KB Shugart SA300 (7.4MB PDF) that cost almost C$300. Its size matches the ST-2900 boards very well, and the system garnered lots of interest whenever I exhibited it. (But I seem to have lost the faceplate for this drive.) On the rear panel we installed a connector for one or two optional external 5¼" floppy drives -- this was especially useful to transfer data to and from my other computers that only had 5¼" floppy drives. We never did install a second 3½" drive even though the box has room and cabling for two drives.

Instead of using an expensive separate CRT terminal, we bought a Term-Mite ST-1000 video terminal board kit from MicroMint and assembled it, connecting it to a 12" NEC JB-1201M (17.5MB PDF) monochrome composite video monitor, and to a keyboard from a surplus Microtel Telidon system. My brother ran the TSC 6809 FLEX operating system on this system.

My brother also successfully repaired a surplus GE TermiNet 1200 printer to use with this system -- I was impressed! Someone had crudely sheared off all the card-edge fingers on its many circuit boards so they could sell the tiny bit of gold, so my brother had to solder on replacement card-edge fingers. The printing mechanism had raised characters moulded on the ends of metal fingers that were attached to a rapidly rotating flexible belt. Little solenoid-operated hammers hit the fingers at exactly the right time as they passed by, achieving approximately one complete line per second (120 characters/sec.), which was quite fast for its time. (I bought this damaged printer for C$100, but one source says an HP branded narrower and slower version of this printer originally cost almost U$5000!)

When my brother upgraded to an Apple IIGS computer he returned this system to me. Later I designed and built the SASI adapter to connect an external 10MB hard drive to this system. It was then used mainly with OS-9/6809 Level I to run my custom accounting software for several years.

Eventually I stopped using the Term-Mite and connected a used Qume QVT-102A CRT terminal instead. I don't remember whether this was because the Term-Mite stopped working, or whether the bugs in its firmware caused me too many problems when used with IMS.

But as sales of my ST-2900 board sets and DMC floppy disk controller cartridges dried up, I had less need to use my custom accounting software, so used my System 2 less and less. Then in 1993 I replaced it with a simpler accounting program I wrote that ran under MS-DOS on my 286 computer. When I moved in September 1998 I put System 2 into storage, until ...

Restoration

I hadn't powered this system up for over 23 years, so didn't know if it still worked. I decided to use my old restored power supply for initial testing because the old switching power supply in System 2 wasn't tested yet. On 2021-Sep-12 I applied power to the CPU+FDC board set and ST-MON 2.04 came alive on the CPU board! A memory test ran for over 2 hours, with no problems.

I then modified the CPU board by replacing the 1488 (U1) and 1489 (U11) with MAX1488E and MAX1489E chips, and removing capacitors C3, C4, C5, C6, to support faster baud rates. Testing the second serial port at 115200 bps verified it was working.

icon to link to photo of DC-DC board top from rear icon to link to photo of DC-DC board top from overhead icon to link to photo of DC-DC board bottom In March 2023 I built a new power supply for testing ST-2900 systems. The DC-DC board contains two small isolated DC-DC converter modules and one LDO to generate -12VDC @ 70mA and +12VDC @ 50mA from +5VDC. It's not pretty, but it works, and is smaller (and hopefully more reliable) than my ancient restored linear power supply.
icon to link to photo of 5VDC switching wall wart icon to link to PDF schematics of DC-DC board A switching wall wart from my old retired D-Link DI-704 router/switch supplies +5VDC regulated @ 2.5A to the DC-DC board, which passes it through to the ST-2900. Schematics are in the PDF file.

I haven't yet tested the two parallel ports, the floppy disk controller, the 3½" floppy disk drive, or the switching power supply, but my guess is they all still work. I'm not as confident about the SASI interface, or about the external hard drive and SASI controller and their power supply. Stay tuned for further progress reports.

The Term-Mite ST-1000 (non-working?) with documentation is available for sale. Make me an offer.

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System 3

icon to link to photo of System 3 enclosure icon to link to photo of front/left/top of System 3 icon to link to photo of rear/right/top of System 3
System 3 pictures (354-480KB .jpg).

System 3 is a 2-board (CPU + FDC) system in a custom aluminum chassis (approx. 5" x 9" x 6"). The cover was cut from my SwTPc system's cover (sorry!). It has a Power-One HTAA-16W-A linear power supply rated at +5V @ 2A, +12V @ 400mA, -12V @ 400mA.

When I built this system in 1990 or 1991 I intended to run it as a diskless system, connecting its serial port(s) to an IBM PC clone, which would run software to allow the ST-2900 to use the PC's keyboard, display, printer, floppy and hard disk drives, etc., similar to the DriveWire software for the CoCo that came out several years later. But I never finished this software.

I wrote a driver for OS-9 to implement a tiny RAM-Disk in the ST-2900's main memory (since this system doesn't have a RAM-512 board). OS-9 was to be booted by converting the OS9Kernel and OS9Boot and RAM-Disk files into Motorola S-Record (S19) file format, then loading them into the ST-2900's RAM via the console serial port using ST-MON's 'L' command and the upload command in a terminal emulation program on the host PC. I don't remember whether I got it all working at that time.

I have recently upgraded and expanded this RAM-Disk software, which now allows booting and running OS-9, NitrOS-9, FLEX, or SK*DOS, on an ST-2900 system with no disk drives connected. Of course loading the operating system via a slow (9600 bps) serial port, and only having a tiny RAM-Disk that can't be saved, is of limited use. But it's been a fun project, and it makes it easy to test an ST-2900 board set if you don't have any floppy disk drives available to connect to it.

I exhibited this ST-2900 system with two borrowed external 5¼" floppy disk drives at the Vintage Computer Festival in Seattle WA in February 2018. I used a Toshiba T2400CS (1994-era '486 notebook computer) with Windows 95 running HyperTerminal as the serial terminal. I demonstrated FLEX and OS-9 running on this ST-2900.

I will soon install an NVRAM/RTC board in this system to allow it to boot and run without any floppy disk drives, but without needing to upload the operating system via a slow serial port. It will provide lots of non-volatile storage for programs and other files, finally making this "diskless" system very useful. But how will I load files onto the NVRAM/RTC board?

I have now written software similar to DriveWire, that I call DSKserv/DSKdrv. DSKserv is a Win32 console mode host program running on a Windows PC that serves FLEX or (Nitr)OS-9 disk images to a client ST-2900 system, while DSKdrv is the FLEX or (Nitr)OS-9 disk driver on the ST-2900. The second serial port on the ST-2900 is configured for 115200 bps and automatic RTS/CTS hardware flow control. Patches to ST-MON allow booting FLEX and (Nitr)OS-9 from local drives or from a remote disk image. This makes a "diskless" system even more capable and easy to use, and makes it possible to get files to (and from) the NVRAM/RTC board.

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"FLEX" was a trademark of Technical System Consultants (TSC).
"OS-9" is a registered trademark of Microware LP.

Last revised 2024-May-09 10:56 PDT.
Copyright 2018- David C. Wiens.


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