KIM-1

The KIM-1, short for Keyboard Input Monitor, was a small 6502-based microcomputer kit developed and produced by MOS Technology, Inc. and launched in 1975. It was very successful in terms of that period, due to its low price (following from the inexpensive 6502) and easy-access expandability.

History

MOS Technology's first processor, the 6501, could be plugged into existing motherboards that used the Motorola 6800, allowing potential users (i.e. engineers and hobbyists) to get a development system up and running very easily using existing hardware. This enraged Motorola, who immediately sued, forcing MOS to pull the 6501 from the market. Changing the pin layout produced the "lawsuit-friendly" 6502. Otherwise identical to the 6501, it nevertheless had the disadvantage of having no machine in which new users could quickly start playing with the CPU. Chuck Peddle, leader of the 650x group at MOS (and former member of Motorola's 6800 team) designed the KIM-1 in order to fill this need.

While the machine was originally intended to be used by engineers, it quickly found a large audience with hobbyists. A complete system could be constructed for under $500 with the purchase of the kit for only $245, and then adding a used terminal and a cassette tape drive. Many books were available demonstrating small assembly language programs for the KIM. One demo program converted the KIM into a music box by toggling a software-controllable output bit connected to a small loudspeaker. As the system became more popular one of the common additions was the BASIC programming language. This required the use of the 8KB memory expansion and was loaded off of tape – a 15 minute ordeal.

Rockwell International—who second-sourced the 6502, along with Synertek—released their own evaluation board in 1976, the AIM 65. The AIM included a full ASCII keyboard, a 20-character 14-segment alphanumeric LED display, and a small cash register-like printer. A debug monitor was provided as standard firmware for the AIM, and users could also purchase optional ROM chips with an assembler and a Microsoft BASIC interpreter to choose from.

Finally, there was the Synertek SYM-1 variant, which could be said to be a machine halfway between the KIM and the AIM; it had the KIM's small display, and a simple membrane keyboard of 29 keys (hex digits and control keys only), but provided AIM-standard expansion interfaces and true RS-232 (voltage level as well as current loop mode supported).

Not long after the KIM's introduction, MOS Technology, Inc. was purchased by Commodore International and production of the original KIM lasted for a while under the CBM label, before it was ended. Chuck Peddle started work on an expanded version, with a full built-in QWERTY-keyboard, cassette tape drive, and monochrome monitor display. The monitor was driven by a new built-in display driver chip, meaning no external terminal was required. The ROM firmware was expanded to include the BASIC as well, so the machine was up and running as soon as the power was turned on. The result was the Commodore PET, launched in 1977 – one of three historic home/personal computers to appear that year; the two others being the Apple II (6502-based) and the TRS-80 (with a Zilog Z80).

Description

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The KIM-1 consisted of a single printed circuit board with all the circuitry on one side. It included three main ICs; the 6502 CPU, and two 6530s containing 1KB of ROM, 64 bytes of RAM, and several I/O lines. An additional 1K (which they described as "a full 1024 bytes") of RAM was included in separate ICs. Also included were six 7-segment LEDs (like on a calculator) and a 24-key calculator-type keypad. Many of the pins of the I/O portions of the 6530s were connected to two connectors on the edge of the board, where they could be used as a serial system for driving a terminal or paper tape. One of these connectors also doubled as the power supply connector, and included analog lines that could be attached to a cassette tape recorder.

Earlier microcomputer systems such as the MITS Altair used a series of switches on the front of the machine to enter data. In order to do anything useful, the user had to enter a small program known as the "bootstrap loader" into the machine using these switches, a process known as booting. Once loaded, the loader would be used to load a larger program off of a storage device like a paper tape reader. It would often take upwards of five minutes to load the tiny program into memory, and a single error while flipping the switches meant that the bootstrap loader would crash the machine. This could render some of the bootstrap code garbled, in which case the programmer had to reenter the whole thing and start all over again.

The KIM-1 included a somewhat more complex bootstrap loader called TIM burned into the two 1K ROMs; this is the "monitor" the name refers to. This monitor software included the ability to run a cassette tape for storage, drive the LED display, and run the keypad. As soon as the power was turned on, the monitor would load and the user could immediately start interacting with the machine via the keypad. The KIM-1 was one of the first single-board computers, needing only an external power supply to enable its use as a stand-alone experimental computer. This fact, plus the relatively low cost of getting started, made it quite popular with hobbyists through the late 1970s.

External links

• The KIM-1 exhibit at the virtual computer museum OLD-COMPUTERS.COM (http://www.old-computers.com/museum/computer.asp?c=149)
• KIM-1 6502 website (http://users.telenet.be/kim1-6502/) – erik.vdbroeck's resource site for the KIM-1, with several HTML'ized manuals and books
• Instructions on building your own KIM-1 (http://www.6502.org/oldmicro/buildkim/buildkim.htm)
• KIM-1 Hints/FAQ (http://zimmers.net/cbmpics/cbm/kim1/kim-hints.txt)