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: Mark-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: Mark-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: Memory Test.pdf [65.6 KB]