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12606B
3-61.
TRACK ORIGIN DETECTION.
3-62.
To determine when the disc has reached or passed
the track origin, first a CLF instruction is performed. This
instruction uses the I/O select code of the disc command
channel. Then an SFS instruction is performed; this in-
struction is also addressed to the disc command channel.
If
the track origin has been passed since performance of the
CLF instruction, a program skip occurs.
If
the track origin
has not been reached, the SFS instruction can be repeated
as often as suits requirements, until the track origin is
reached.
3-63.
The track origin check does not interfere with a
disc data-transfer operation, if one is taking place.
Section III
3-64.
SCP FLIP-FLOP CHECK.
3-65.
As a computer trouble-shooting procedure, a
check can be made of the SCP flip-flop, situated on the
command channel interface card. To make this check, an
SFC instruction is addressed to the disc command channel.
If
the SCP flip-flop is clear, a program skip takes place.
If
the flip-flop is in the set state, no skip occurs.
3-66.
Performance of the SCP flip-flop check does not
interfere with a disc data transfer operation, if one is taking
place.
3-7/3-8
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