Technical data

If an error occurs, (one or more links not in the data transfer phase), the ZP
station list can be read out at any point. If all the links are functioning
correctly in the data transfer phase, the RECEIVE HDB for the ZP station
list is disabled.
A further distinction must be made as to the mode (FREE or
CYCLE-SYNCHRONIZED) in which the station list is evaluated, as follows:
FREE:
the station list is updated continuously by the CP.
CYCLE-SYNCHRONIZED:
the station list is updated by the CP at the point when the HDB RECEIVE
with job number 211 is called in the control program (ZP receive)
B8976060/02 Communication with Cyclic I/Os
10 - 19 Volume 1