GMX 6809 CPU III

The GMX 6809 CPU III from GIMIX Inc. was a high-performance 6809 processor card for the SS-50 bus. It was designed specifically to run Microware's OS-9/6809 Level II operating system with minimal overhead, to maximize performance.

GMX 6809 CPU III features:

• 2 MHz MC68B09 processor
• MMU/DAT (Memory Management Unit with Dynamic Address Translation) uses a 256x12 SRAM to store 8 task maps (1 system, 7 user), each addressing 32 2KB pages
• 20-bit physical address for 1MB range
• attributes for each memory segment: write protect, memory not allocated, hardware single-step
• full 64KB (65536 bytes) available for each user task
• separate Supervisor and User states
• automatic switching to Supervisor state in response to hardware and software interrupts
• I/O only accessible from supervisor state, not user tasks
• automatic interrupt masking
• DMA for high speed memory-to-memory and memory-to/from-I/O transfers via MMU/DAT, custom design using PAL chips
• watchdog timer for automatic recovery from certain illegal instructions
• calendar/clock (146818), with on-board battery backup
• programmable timer module (MC68B40), with precision time-base and connector for external signals
• 28-pin socket for 2KB or 4KB or 8KB EPROM
• 2KB SRAM, with on-board battery backup
• missing cycle detector monitors AC power input for loss of power
• undervoltage detection on +8VDC board supply
• gold-plated SS-50 bus connector
• 1984 price list showed the GMX 6809 CPU III with OS-9-GMX III costing U$1698.01

The GMX 6809 CPU III had similar capabilities as the CMS 9639 (for the EXORbus) from Creative Micro Systems.

Intelligent serial I/O boards for the SS-30 bus allowed many users to simultaneously use the system without bogging down the main processor with interrupts for each character.

A separate SS-30 bus CRC Generator board was available to speed up calculating the 24-bit CRC that each OS-9 memory module contains. Using the memory-to-memory DMA on the GMX 6809 CPU III, an 8KB module could be checked in 8.5 msec. vs. 455 msec. or more using the software routine. But it required masking interrupts for the duration of the DMA transfer to the CRC Generator because it wasn't reentrant. (Why didn't they rather set a "busy" flag to prevent starting another transfer until the first one was completed, to avoid masking interrupts?)

Does anyone have or know where to find a boot image for OS-9-GMX III? It would likely consist of the OS9Boot file on floppy disk or on a hard drive, as well as part of the kernel in an EPROM.

Søren Roug has posted scanned copies of several user manuals relating to the GMX III system, such as the DMA III disk controller and the OS-9 GMX III Support ROM. Unfortunately he hasn't found any boot disk image for the GMX III.

The history of GIMIX would also be very interesting. It appears that the founder, Richard Don, passed away in 2005, but I will try to contact his family to see if they would be able and willing to provide me some history.

(Click on a picture for a larger version.)

B&W ad photo (1.7MB .png) and color ad photo (525KB .jpg)

Pictures of Gene Buckle's GMX system (155KB-855KB .jpg)

Gene Buckle gave me permission to post pictures of his GMX system. The six pictures are:

• GMX 6809 CPU III - note the heatsink on the 6809, and 14 custom PAL chips!
• GMX DMA III - 5" and 8" floppy disk controller with DMA
• GMX 256KB SRAM - with on-board battery backup
• GMX motherboard - SS-50/SS-30 bus
• GMX SIOP3 - intelligent 3-port serial card
• GMX baud rate generator card

The 2764 EPROM on the SIOP3 board says "OS-9 V2.00 (c) 1983 MSC". I wonder if that means it is actually running a separate copy of OS-9 Level I on this I/O board? The purple chip at the bottom is an AMD Z8038 Z-FIO, which is a dual-port 128-byte FIFO buffer that provides an interface between the 6809 on the SIOP3 and the 6809 on the GMX 6809 CPU III.

	GMX 6809 CPU III User's Manual. (scanned image, 5.8MB .pdf)
	GIMIX CRC Generator Board User's Manual. (searchable scanned image, 207KB .pdf)
	Microware OS-9 Level Two System Designer's Guide (handwritten annotations are mine). (scanned image, 5.2MB .pdf)

"OS-9" is a registered trademark of Microware LP.

Last revised 2024-Apr-04 12:42 PDT.
Copyright 2019- David C. Wiens.