Jonathan A. Titus

Microcomputer Pioneer

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Lesson 5: CPU and Memory

From the original article in Radio-Electronics
by Jonathan A. Titus
The Central Processor Unit (CPU) module contains the microprocessor IC and the extra circuitry used to interface with the rest of the computer. It is important to note that the 8008 microprocessor has been fabricated as an MOS circuit and the outputs will only drive one low-power circuit of the 74L series. Each output is buffered with a 74L04 inverter before it is used. The main, 8-line input/output bus, or I/O bus is also buffered by two 7404 circuits to give the TTL signals a high fan-out.
Read More: Adobe Acrobat PDF FileMark-8 Construction.pdf, p.2 [2.54 MB]

The Memory module uses the widely available 1101 type of semiconductor, integrated circuit memory. The 1101 random access memory or RAM is organized as a 256 x l-bit memory, so eight of the 1101 type memories are used to give us 256, eight-bit words. This is the minimum configuration necessary for the operation of the Mark-8. Each memory module can hold 32 of the 1101 memories for a total of 1024 or 1k words of storage . Up to four Memory modules may be used with the Mark-8, giving us a maximum 4k of storage space. More than enough for most applications.
Read More: Adobe Acrobat PDF FileMark-8 Construction.pdf, p.3 [2.54 MB]

From the Mark-8/Micro-8 Computer User Group Newsletter
by Walter M. White
"Memory Test Program for Mark-8"
Purpose of the program is to thoroughly check the semiconductor memory used with the 8008 for ICs that will not accept data correctly or have problems in their internal address decoding circuitry.
Read More: Adobe Acrobat PDF FileMemory Test.pdf [65.6 KB]