Peripheral Technology PT-69 6809 Single Board Computer
The Peripheral Technology PT-69, which was only 50% larger than the ST-2900
CPU board, was probably the main competition
for the ST-2900.
The PT-69 started shipping almost a year before the ST-2900. It appears that one
of their main design criteria was to make it totally compatible with software for
SwTPc SS-50 bus systems, whereas I was willing to forsake some compatibility for
superior features. (In any case, the effort to make software compatible with
the ST-2900 was usually fairly minimal.)
A comparison of the ST-2900 vs. the original PT-69:
- processor: both used a 1 MHz Motorola 6809E
- type of memory: both used eight 64kbit DRAM chips
- DRAM control: both used the Motorola Synchronous Address Multiplexer (SAM/MC6883/SN74LS783)
- memory management: neither implemented a MMU/DAT that would have allowed OS-9 Level II
- I/O address space: 96 bytes (more than enough) vs. 4KB (most of it wasted)
- EPROM: mapped out during normal operation (except for 32 bytes) vs. 4KB
address space always used
- maximum EPROM size: 8KB (up to 64KB with board modifications) vs. only 4KB
- usable RAM: 63.75KB (very important to me) vs. only 56KB
- serial ports: one 2681 DUART (2 ports) vs. two 6850 ACIA
- parallel ports: one 6522 VIA vs. one 6821 PIA
- software compatible with SwTPc: no vs. yes
- floppy disk controller: 1793 vs. 2797
- floppy disk data separation and write precompensation: digital (no adjustments) vs.
analog (requires adjustments)
- side flag in floppy disk ID Record: standard vs. non-standard
(but SwTPc compatible)
- can read/write/format disks with either type of side flag: yes vs. no (a real problem)
- time-of-day clock: no vs. yes (MC146818)
- number of 16-bit counter/timers: 3 vs. 0 (but clock chip can generate a periodic interrupt)
- number of crystals: 3 vs. 2
- expansion connector: yes (60-pin) vs. none
- size: two 3.9" x 6.3" boards vs. one 5.5" x 6.5" board
- PCB: 2-layer, soldermask both sides, silkscreen one side vs. 2-layer,
no soldermask or silkscreen (based on picture in ad)
- initially available assembled/tested: no (but was later) vs. yes
- initial price: U$83 (CPU+FDC bare boards with EPROM) vs. U$295.95 (assembled/tested)
At first only TSC's FLEX operating system was available for the PT-69, but later they also
offered OS-9 Level I and STAR-DOS.
There are some details I don't know. How did the PT-69 generate its baud rate clocks? My
guess is that they might have used a 14.7456 MHz crystal for the SAM chip, thereby running
the CPU at only 921.6 kHz, and picked off the selected 16x baud rate clocks from a /3 and
/2 divider chain fed by the 3.6864 MHz output of the SAM chip. Did they implement a periodic
interrupt to support FLEX printer spooling and OS-9 multi-tasking? If so, did they use the
MC146818 to generate it? At what frequency? Did the clock chip have battery backup circuitry
and a connector for an external battery, or an on-board battery holder?
The only information I have found so far on the PT-69 is from ads and reviews in '68' Micro
Journal. If you have more information on the original PT-69 board, such as color photos,
user manuals, schematics, or EPROM dumps or listings, please
The editors of '68' Micro Journal reviewed the PT-69 on pages 19-21 of the
November 1984 issue.
Several users wrote in with fixes for the PT-69's problem with incompatible disk formats,
such as pages 38-40 in the
issue, and pages 49-51 in the
(Click on a picture for a larger version.)
|Ad in October 1983 '68' Micro Journal.
"FLEX" was a trademark of Technical System Consultants (TSC).
"OS-9" is a registered trademark of Microware LP.
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Last revised 2020-Mar-22 16:42 PDT.
Copyright 2020 by David C. Wiens.