The KIM-1 was Commodore first real computer. But the KIM-1 was designed by the Company MOS. MOS was founded in 1974 by 8 former employees of Motorola. Two of those people were Bill Mensch and Chuck Peddle. The new company was called MOS Technology and it started development on the 6501 chip. This was a microprocessor that was pin compatible with the 6800 chip from Motorola. The internal design was different but Motorola sewed MOS for copying there design. MOS and Motorola settled this disagreement and the 6501 was dropped. MOS went on with designing there new processor. This was the 6502. The 6502 is one of the most important microprocessors ever made. The driving force behind the development of the 6502 was Chuck Peddle. Now the 6502 was born MOS designed a complete computer that used the 6502. The KIM-1 was born. But in the same year the company was taken over by Jack Tarmiel's company Commodore. There are KIM-1's with MOS on the motherboard but the later had the Commodore and the MOS name on the motherboard.
The components:
The KIM-1 is a real computer but it's nothing compared with a modern PC. The KIM has the following major parts. The 6502 microprocessor, Two 6530 I/O chips, 1 kbyte RAM, 2 kbyte ROM, a 6 digit 7-segment LED display. The rest of the component are simple logic components.
The 6502 technical specifications:
Data bus: 8 bits
Address bus: 16 bits
Interrupts: IRQ, NMI, RDY
Speed: 1 MHz
Instructions: 151
The 6502 is microprocessor. Inside a microprocessor all kinds of binary manipulations can be made on data. To get data in and out of the microprocessor a data bus is needed. The data bus of the 6502 is 8 bits wide that means that it has 8 pins that can connect with memory outside the 6502. The 6502 works like all other processors with the binary system. That means there are only 2 possibilities on or off. This will be shown as a 0 or a 1. This is called a bit. If you got a 8 bit wide data bus then the possibilities are 00000000 to 11111111. A value of 8 bit wide is called a byte. In the normal decimal system that is 0 to 255. All processing is limited to the numbers 0 to 255. If you need bigger numbers you will have to chop the big number into little parts.
But there is also something needed to point at the location of the data. This is called a address bus. On the 6502 the address bus of the 6502 is 16 bits wide. With 16 bits you can make numbers between 00000000 00000000 and 11111111 11111111. Or in decimals between 0 and 65536. The 6502 can address 64 kbyte of memory. Keeping in mind that the KIM-1 has only 3 kbytes of RAM / ROM memory the address bus is big enough.
Besides the Data and Address bus the 6502 has also interrupts. An interrupt is a stop-sign. The processor can be halted with an interrupt.
The system speed of the KIM-1 is 1 MHz. This means that there are 1 million actions per second that are processed. So the 6502 processor can do 1.000.000 action every second. The fasted instruction takes only 2 actions but the slowest instruction takes 7.
The 6502 has instructions. The number of instructions is 151 but there are in theory 255 instruction possible. Programmers found extra instructions by experimenting. But these are actually defects that are build into the chips and are not real instructions. There are instructions that only move data like LDA (Load the accumulator with a value) but there are also instructions that will calculate data like ADD (ADD a value to the accumulator) Also there are instructions the manipulate a value like ROR which shifts the bits a place to the right.
The 6530 technical specifications:
Data bus: 8 bits
I/O: 2 x 8 bits (bi-directional)
Timer: programmable
RAM: 64 byte
ROM: 1 kbyte
The two 6530 are the connection with the outside world. The keyboard is read with these chips. The display is also driven by the 6530's. To save your programs there is also a connection for a cassette recorder. And even a teletype connection is available. Almost all of the IO are also available on the edge connectors.
Because the 6530 has it's own ROM there are different types of 6530. MOS have produced different 6530 for specific tasks or other companies.
RAM / ROM:
Nowadays 1 kbyte of RAM is a joke but in 1976 this was huge. RAM is used to store your own program code. RAM can be written and read. RAM stands for Random Access Memory. There is also 2 kbyte of ROM. In this ROM is a program that runs the KIM-1. It takes care of reading the keyboard does the display and the save and load commands. Also it has a machine language assembler to help you to type in your machine language program. ROM can only be read. ROM stands for Read Only Memory. The ROM keeps it's program even when the power supply is disconnected. RAM loses all it's data when this happens.
Keyboard / Display:
To make a complete computer you will need a way to interact with it. Input from the user is done via a simple keyboard with the hexadecimal numbers from 0 to F, a reset button, some keys for programming and a on/off switch.
The display is made up from six 7-segments LED displays. Because the microprocessor can access the individual segments on each display via the 6530's you can display more than 0-9.
On the photo the KIM-1. This is a revision-G from November 1978
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