Technical information

Micro-KIM Users Manual
©
(

As a result of keeping much of the original design and the fact that there are several 7 segment displays, the
Micro-KIM uses a lot of resistors. While resistors don’t add much to the overall cost of the board, the board size
is affected by this. Originally, the goal was to get the Micro-KIM as small as 4” X 4” but because it is a kit with
thru-hole components it was just impossible to get the board down that small.
The onboard RS232 interface is the same circuit used to convert the TTY circuit back in 1976 into a more
common RS232 level format. The original circuit was to use -5V which created a problem since the Micro-KIM
runs off a single 5V source. The circuit allowed for the possibility to use ground instead and with several tests,
the circuit worked with ground. This was huge because if it didn’t work, the TTY/RS232 interface would have
required extra circuitry to generate the -5V required.
The Micro-KIM has an 8K RAM chip onboard but only 5K is used. The reason is simple. The decoding scheme
of the original KIM-1 decoded eight 1K blocks, of which only 1K was used onboard the KIM-1 for RAM and
3K for ROM and I/O. This leaves room for 4K of additional RAM without any further decoding. I simply used
an 8K RAM IC to replace the five 1K blocks available for RAM. This means that 3K of RAM in the onboard
RAM IC is wasted but it is necessary to keep compatibility with the original KIM-1.
The memory decoding scheme of the Micro-KIM is an exact match to the KIM-1, therefore, the system has a
repeating stage of memory every 8K. In other words, the 6502 doesn’t know the difference from $0000 and
$2000. Anything you store in $0000 will show up in $2000 and visa versa. This can be stopped with expansion
by re-decoding memory into 8K blocks and only activating the first 8K when it is directly addressed. For now,
just know that if you see an address such as C12F on the display, that isn’t the actual address being accessed.
The display is controlled by a 6532 RIOT I/O chip and the monitor keeps the current address and data
displayed. When you first power up your Micro-KIM you probably won’t see anything on the display. This is
normal since the microprocessor needs a reset to get running. There is no auto-reset circuit on the KIM-1
therefore there isn’t one on the Micro-KIM either. Pressing RS (RESET) on the keypad performs a system
RESET on the Micro-KIM and starts the system up.