Request : How do AS-I module outputs react in the event 
   of communication failure?

Suggestion : In the event of a communication failure all AS-I outputs are
   set to ''LOW'' within 20 to 100 ms.
   Conditions of outputs prior to failure are retained in the process image of 
   the CPU and will be reinstated after restoration of communication.
   In the event of bus failures the user program must cater for reinstatement of
   outputs in the process image.
                                                                                

Request : The AUTOPROG function is activated as soon as a
   module fails. After replacement of the module it will automatically be 
   addressed with the previous address.
   Is this also the case with the 8-input compact module?

Suggestion : The AUTOPROG function is not possible with the 
   3RK1200-0DQ00-0AA3 (8-way digital input) module.
   Automatic addressing of a replaced slave is only possible if
   - only ONE slave failed
   - the replacement module is exactly the same type as the one that failed
   - the new module has the address ''zero'' (''null'')
   If only one of these conditions are not fulfilled, AUTOPROG is not possible. 
   This is indicated by the LED ''CONFIG ERROR''.
   The 8 I modul occupies 2 slave addresses.
   In the event of slave failure the following happens:
   - yellow LED (CONFIG ERROR) and green LED (AUTOPROG) light up. Theoretically 
   the AUTOPROG function would be possible now. However as soon as you isolate 
   the module from the bus, 2 slave addresses are missing. One of the above 
   conditions is not available anymore and the green LED gets dark.
                                                                                

QUESTION:
What could be the reason for sporadic slave failure on the AS-I bus?

ANSWER:
Check the actual length of the AS-I line. A typical error with AS interface is exceeding the maximum permissible line length of 100m with using an extender or repeater. If the maximum length is exceeded, this might lead to sporadic or permanent slave failure on the AS-I bus.

Tip:
When checking the line length, don't forget to take into account the length of the AS-I cables that you have installed in the switchgear cubicles. Very often these cable lengths are forgotten.