Limit switches in EPICS

EPICS has the unfortunate characteristic that it reads the status of limit switches (and updates the motor fields HLS and LLS) only when the motor is moving. That is, if you manually close a limit switch and look at either the HLS or LLS limit status values, EPICS will not show any change unless you ask the motor to move.

As noted in Table C.2, a closed circuit between the limit input and ground means ``not at limit'', while an open circuit means ``at limit.''