(This page is still under construction.)(Currently in design stage)
The 6809-Tiny6 is a powerful 6809E/6309E single board computer (SBC) in only 6 square inches! It provides most of the functionality of the ST-2900 CPU and RAM-512 boards, but in less than 12% of the board area, using less power, yet runs 2 or 3 times faster.
This board is probably the smallest possible for the features provided when using thru-hole devices (or sockets) and using an actual 40-pin microprocessor instead of an FPGA emulation. In order to achieve the small size I placed some components on the bottom side.
I had hoped to entirely avoid any surface mount components, but the PCB manufacturing service I was planning to use for the prototype, ExpressPCB's 4 Layer MiniBoardPro Service, only allows 350 holes, and my layout had 370. In order to eliminate some holes I replaced two 8-pin thru-hole resistor SIPs with eight 0805 SMT resistors, and a thru-hole pushbutton switch with an SMT version. It now has exactly 350 holes. But if I re-create the layout with KiCad (which I have started to learn) I won't have that limitation.
There were a few other features I would have liked to add to the board, but every pin on the CPLD is already used, and I didn't want to use a larger CPLD (in a larger package) for this board. Actually, the ATF750C CPLD is a perfect fit for this design, in terms of numbers of pins, speed, and available package. (Unfortunately, most low-cost device programmers don't support the ATF750C, only more expensive programmers such as the Xeltek SuperPro, eeTools ChipMax2, and Dataman 40Pro Universal ISP Programmer.)
I have some ideas for a small optional daughterboard for the 6809-Tiny6 that would significantly speed up loading OS-9 memory modules by verifying the header parity byte and 24-bit module CRC in hardware rather than using the kernel's software routine. But it would require surface mount components.
(Click on a picture for a larger version.)
|Tentative board layout.|
I actually started designing several tiny 6809 single-board computers (SBC) over 34 years ago. One of them (2.7MB .zip) was exactly the same size as the new 6809-Tiny6: 2.4" x 2.5". But it only had 32KB SRAM instead of 512KB, 16KB EPROM instead of 32KB EEPROM, 1 serial port instead of 2. However, it was going to have a full expansion bus, which the Tiny6 doesn't have (yet). I never built any prototypes, and didn't create any PCB layout, so don't know whether I could actually have routed all the signals, especially with a 2-layer PCB, since 4-layer boards were still rather expensive back then. I also didn't have any PCB CAD software at that time, so don't know how I would have generated the PCB layout.
"FLEX" was a trademark of Technical System Consultants (TSC).
"OS-9" is a registered trademark of Microware LP.
"1-Wire" is a registered trademark of Maxim Integrated.
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Last revised 2022-Jun-01 12:31 PDT.
Copyright 2020-2022 David C. Wiens.