Jonathan A. Titus

Microcomputer Pioneer

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Lesson 1: Intoduction to the Mark-8

From the original article in Radio-Electronics
by Jonathan A. Titus
The heart of the Mark-8 Minicomputer is an Intel 8008 microprocessor IC that contains all of the arithmetic registers, subroutine registers and most of the control logic necessary to interface the microprocessor with semiconductor memories as well as input and output registers. Standard TTL type IC's are used throughout and commonly available 1101. 1101A and 1101A1 type memories are used for the central storage. The microprocessor with its associated logic will be refered to as the central processor unit. or CPU.

The central processor unit is an 8-bit parallel processor. A string of eight binary bits. D7 through D0 is used to indicate the instruction data or memory locations. Rather than repeat, "eight bits of binary data " , we refer to the eight bits as a byte. As you will note, some of the instructions take up to three bytes of data and they are, therefore, called three-byte instructions. The computer takes 20ms to execute each byte of these instructions, so the time to execute any of the basic instructions may vary from 20 to 60 ms. The time that the computer takes to execute one byte of the instruction is called the computer's cycle time. Most minicomputers have a cycle time that is about ten times faster than the Mark-8, but this will not restrict the use of this Minicomputer in most situations.

The Intel 8008 microprocessor provides us with some sophisticated features, only found on larger, more costly computers. These include a pointer register, interrupt pointers and a stack register for multiple subroutines.
Read More: Adobe Acrobat PDF FileMark-8 Construction.pdf [2.54 MB]

Read More: Adobe Acrobat PDF FileMark-8 Schematics.pdf [7.88 MB]

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