Why do I get IP communication errors from time to time on a PCD2.M554x?
The constellation of the CPU of the PCD2.M5540 and the on-board switch which is leads to the situation that (very few) telegrams may be lost. This fact can lead to the situation that the Error LED of e.g. a SASI IP Master FBox (or any communication FBox) turns red after a certain time of running communication.
The "SASI IP Master" FBox (or every other IP-communication related FBox such as a Modbus/IP FBox) turns red after several minutes of running communication. The send and receive FBoxes do not indicate an error (as it is most likely not seen; it is only red during one retry, thus around 250ms).
In fact the phenomenon of lost telegrams (around one out of 6000) is not only present when using Ether-S-Bus or Modbus TCP/UDP but affects all IP communciation of the PCD2.M554x. It can easily be observed when using e.g. Ether-S-Bus or Modbus (because of the red LED in case of a retry), but also other telegrams such as http telegrams can be lost (but in this case the TCP level will automatically re-send the lost telegram).
This phenomenon is caused by a bug of the used Freescale processor in relation to the IP switch which is used on the PCD2.M5.
Unfortunately there is no solution available for this phenomenon.
Please note that the impact of this situation is not serious as all the communication protocols will automatically generate a retry which will be answered correctly. The only "damage" is a red LED and a single delay of the response time in case of a lost telegram.
PCD2 / M5xxx
Last update: 31.05.2015 16:32
First release: 26.07.2010 16:23