This board is targeted to 6809 based systems which have a 4K EPROM window from F000 to FFFF. By default, the EEPROMs included with all our systems are 8K (28C64) because it’s easier for me to stock one EEPROM instead of multiple ones. The lower 4K is not accessible, and SBUG is in the top 4K.
As some of you know, we’ve been looking at getting a port of OS/9 and while working with the OS/9 experts it was decided that a custom EPROM image with most of OS/9 in it would be a better solution that have 4K of SBUG and then using a lot of RAM for the OS. I didn’t want to make a customer choose between flashing either OS/9 or SBUG, so it was suggested to make a small add-on board with DIP switches to select which image to load.
Here is that board:
SW1 controls A12 and SW2 controls A13, so by setting them appropriately and with the right size EPROM, this board allows up to four boot images to be in memory from E000 to FFFF. Since I use 8K EEPROMs, only two images are available, but a customer can also use a 28C128 which allows four images.
The price for this board assembled and tested without an EEPROM is $20. Kit is $15, and a bare board for $10. Free shipping in the US, of course.
I can hear your next question: “So is OS/9 available?”
No, but extremely close. Boisy Pitre and I worked at VCF SE and made a lot of progress. I made changes to the EEPROM code and Arduino code, as well as to the motherboard to allow everything to work. He did all the code changes in NitrOS/9 to support the Corsham Tech boards. I’ve had a preliminary version running for about a month now and it’s very nice. Boisy is working to get the changes into the official distribution and then it will be available. In the picture above, SW1 selects SBUG or NitrOS/9 boot… ON is Flex, OFF is NitrOS/9.
Close, very close.