IBM Series 1 User Manual page 41

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either 1) does not become active with service gate
active, or 2) does not deactivate after it has become
active, then a machine check occurs and the channel
activates the Halt or MCHK line. If the device
attachment adheres to the specified times over which it
has control, the total duration of the sequence will be
within this channel timeout under normal operation.
GA34-0033