Jonathan A. Titus

Microcomputer Pioneer

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Lesson 9: Bus and Input-Output

From the original article in Radio-Electronics
by Jonathan A. Titus
The Data Input Multiplexer module controls the now of all data into the computer. All data going into the computer is placed on the I/O bus during the IN cycle signalled by the IN signal. Since data may be coming in from a number of different experiments or sources, we must have some means of selecting which data is fed into the CPU . Two basic multiplexers are used for this precise gating of data . The two 8263 quad, three-line to one-line multiplexers control which of three sets of input lines are selected . Note that two sets of these input lines are input ports 0 and 1. These are the two external data input ports. The third set of data input lines comes from the memory. Data or instructions in the memory, all go through the multiplexer and into the CPU.
Read More: Adobe Acrobat PDF FileMark-8 Construction.pdf, p.3 [2.54 MB]

The Output Latch module is used to send data from the computer to some external device or instrument, such as a teletype or perhaps the Radio-Electronics TV Typewriter (Radio-Electronics, September 1973). Four output latches are provided on the Output Latch module and two of these modules may be used with the Mark-8. The second module may, however, only use three of the output latches.
Read More: Adobe Acrobat PDF FileMark-8 Construction.pdf, p.4 [2.54 MB]

The Mark-8 bus included 40 lines, divided into power lines, 3 input and 8 output lines, memory address lines, interrupt lines, and multiple lines carrying control signals. See the one-page summary "Mark-8 Bus Signal Description" by L.L. Plate
Read More: Adobe Acrobat PDF FileMark-8 Bus Signal Description.pdf, p.4 [32.5 KB]