Siemens S5-135U/155U System Manual page 281

Design
The COR 923C is designed as a plug-in PCB in double Eurocard format.
Two 48-way Series 2 blade connectors serve to connect the module to the S5
bus in the subrack.
The front plate width is 1 1/3 standard plug-in stations.
A mode switch with three settings is fitted in the front plate for other
operator functions.
Faults are indicated by five small red LEDs.
There is a recess with cover in the upper third of the front plate. By removing
the cover, you can operate the DIL switches to set parameters for the module.
You can connect the COR 923C via a 15-pin front connector to a
programmer, OP, operator control panel or the CP 530 and CP 143.
Principle of The COR 923C cyclically allocates a bus enable signal to each of the two to
Operation
four CPUs in the S5-135U/155U PLC. Only during this time can the relevant
CPU utilize the common S5 bus.
The assignment of bus enable signals takes place in time-division multiplex
operation. On the COR 923C, you set the number of CPUs with DIL
switches. The enable time for access to the S5 bus is preset at 2 ms for all
CPUs. If the bus enable signal has been emitted by the coordinator for a
CPU, this CPU can extend the enable time with the bus lock signal. However,
the user has no influence on this.
The bus enable assignment sequence begins with CPU 1 after the Reset
signal is removed by the power supply, and enables the CPUs in the
following order according to the preset number of CPUs:
CPU 1, CPU 2, CPU 3, CPU 4, CPU 1, CPU 2 etc. (see Figure 6-7)
System Manual
C79000-G8576-C199-06
Multiprocessor Operation/Coordinators
6-19