Microbox II 6809 Single Board Computer

The Microbox II single board computer was a product of Micro Concepts in England, and was designed by Dave Rumball.

The Microbox II featured:

• 1-2 MHz 68B09E microprocessor
• 60KB DRAM (supported by a 6883/SAM chip)
• 8KB EPROM (4KB mapped out when running FLEX)
• 2 RS-232 serial ports (WD2123 DUART)
• parallel printer port (buffered)
• parallel keyboard port
• time-of-day clock/calendar (146818) with on-board trickle-charged battery
• monochrome video display (NEC 7220A controller): text (84x24 or 108x24), graphics (768x576) with drawing and fill commands
• 128KB DRAM shared by video display and RAM-Disk
• 64KB EPROM-Disk plus on-board EPROM programmer
• single/double-density floppy disk controller (WD1770) for 2 drives
• 50-pin user expansion bus (buffered)
• 9.5" x 12.0" PCB (2-layer, no soldermask or silkscreen)
• FLEX operating system supported
• cost U$190 for a bare board plus monitor in EPROM and system disk

At first the only information I could find on the Microbox II (MB2) was from an ad in '68' Micro Journal on page 56 in the March 1986 issue. But in March 2020 a member of the SS50 & SS30 Computer Bus Chat Facebook group page posted a picture of his Microbox II, and another member pointed me to additional information. Just a few weeks later I found another Microbox II owner in South Africa who has documented his board. Thanks Jarmo and Nadim and Wouter! Additional information has now also been posted to Dave Rumball's MB2 GitHub page.

The Microbox II was featured in a series of articles in the UK edition of Electronics Today International (ETI) magazine:

• pages 27-29 in the December 1985 issue
• pages 36-39 in the January 1986 issue
• pages 31-37 in the February 1986 issue
• pages 47-49 in the March 1986 issue
• pages 49-51 in the April 1986 issue

Philippe Roehr has recently re-created the PCB layout of the Microbox II, with a few enhancements, and is making the Gerber files available if someone wants to build a new board.

Several decades after designing the Microbox II (MB2), Dave Rumball has done it again with the MB2K2, a tiny 80mm x 80mm board with custom hardware and software that aims be a complete emulation of the MB2 to the point of running the original’s software without modifications. Most of the individual LSI chips in the MB2 are emulated by one of the 16 RISC cores in the XMOS XU216 SoC (System on a Chip). The emulated 6809 processor runs at approx. 8 MHz. The 'MON09' monitor ROM includes FlexNet drivers and commands to mount remote drives, so it's possible to boot and run completely from remote disk images, as well as using the on-chip PROMdisk and RAMdisk. More information can be obtained from his MB2K2 GitHub page. Dave also has information on the MB2, MB2K, MB3, and Image10 in his Microbox GitHub archive.

(Click on a picture for a larger version.)

Picture of top side (168KB .jpg).

UK 68 Micro Group disks for the Microbox II. (3 .dsk files in 40T/SS/SD FLEX format, 80KB .zip)

"FLEX" was a trademark of Technical System Consultants (TSC).

Last revised 2024-Apr-04 12:41 PDT.
Copyright 2019- David C. Wiens.