Technical information
Micro-KIM Users Manual
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How the Micro-KIM came to be
For those of you familiar with Briel Computers, you know about the replica 1 computer. In short, it is a single
board computer designed to replicate the Apple 1 computer. For the last 3 years I’ve been searching for a way
to get this computer priced under $100 so more people can enjoy building them. With parts going up in price
I’ve found this to be impossible. So, I went searching for a different platform to replicate.
Why redesign the KIM-1? Why offer it as a kit? Because there are still people out there who like to build and
work with kits like those offered in the 1970’s and 80’s. The KIM-1 has been called the “first single-board
computer” by many and was created by Chuck Peddle of MOS as a development board for the 6502 CPU. What
better computer to replicate than the first computer designed for the 6502?
The major problem with replicating the KIM-1 was the 6530 RRIOT IC’s which have custom ROM’s
embedded in them. These are no longer available and are difficult to locate. The KIM-1 used two and each one
held a section of the monitor program. The solution was to use an external EPROM and a 6532 RIOT which is
very close to the 6530 but with some minor differences. This required a tricky addressing scheme I developed to
replicate the exact addressing as the original KIM-1 so programs would work the same.
The next decision was to drop the second 6530 (6532) to reduce chip count. This was an easy decision because
it can be added later in an expansion. The problem was the 2
nd
6530 on the KIM-1 held 64 bytes of RAM. As
luck would have it, the 6532 has 128 bytes of onboard RAM vs. the 6530 which only has 64 bytes. I decided to
use all 128 bytes available on the 6532 in place of the 128 bytes used in 2 6530’s in the KIM-1.
There is no source for replacement keypads used on the KIM-1 so I decided to just go ahead and put the
keyboard onboard and use tactile switches with silkscreen labels above them for identifying the buttons. This
wasn’t perfect but it really helped with the cost and keeping the Micro-KIM to a small footprint.
The last major decision was difficult to make but I felt it was necessary. The expansion slots on the KIM-1 were
a disaster. They held unnecessary signals, orientated in a difficult setup and spaced far apart on the board. After
debating this one for a long time, I decided to just dump the original interface and create a 40 pin header with
all the major signals needed for expansion. Keeping as much of the original signals as possible, yet getting
everything needed all in a 40 pin setup was difficult. It is very possible to recreate the original expansion
connectors with this setup but there are a few minor signals missing.
Finally I’d like to thank my good friend Rich Dreher for helping me out more than I hoped for on this project.
Not only did he redo the board layout for me and help clean up the schematics, he pushed me to add the TTY
RS232 interface onboard to add value and much needed I/O onboard. Without Rich’s help this project would
not be what it is today.
I hope you enjoy your Micro-KIM and that it brings you as much happiness building and using it as I did
designing it.
Vince Briel