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When the CPU wishes to send a command to the peripheral, it writes a value
into the command port. There may be many possible commands. Here are the
most important, encoded using both numbers and words:
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001
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START
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begin reading the tape and transferring data to the CPU
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010
|
HALT
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stop reading the tape
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011
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REWIND
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physically rewind the tape back to the beginning
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100
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ALERT
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flash a light on the external case of the tape record to alert the
human who is operating the device
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101
|
QUERY
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have the tape reader tell the CPU what state it is in
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110
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PAUSE
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suspend sending data until further notice
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