1) Unit ID 1: Indicates the equipment sending the signal. When
supporting Set ID by the command 1, 4 bits of low ranks of Set ID are
set up.
2) Unit ID 2: Indicates the equipment receiving the signal. When
supporting Set ID by the command 1, 4 bits of higher ranks of Set ID
are set up.
* Set ID : it is the apparatus number assigned to each plasma monitor.
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