Why do I sporadically get communication errors when connecting a PCD/PCS in "Secure S-Bus Data Mode"?

FAQ #101180

 

Symptom
A PCD or a PCS connected with another system (e.g. PC or another PCD system) using the "Secure S-Bus Data mode" does not answer a telegram from time to time. This can e.g. be seen by a red LED on transmit or receive FBoxes (or in case a PC is used, by interpreting the tracewin files).
This phenomenon can be observed on PCD1.M1x5, PCD2.M150, PCD2/4.M170 and PCS1 systems (with firmware which are supporting the "Secure S-Bus Data mode"). Saia PCD® COSinus based systems (PCD2.M480, PCD2.M5xx0 and PCD3) are not concerned.

Reason
The reason for this behavior is that the PCD/PCS does not correcly answer telegrams where the sequence number in the secure S-Bus Data Mode header is 0xC5h. This is the case in every 255th telegram.
(The character "C5" should be replaced by "C5 01" but this is not done).

Solution
Please refer to the table below for firmware version which do correctly handle the "C5" and therefore the symptom described above is avoided.

System	Firmware
PCD1.M1x5	0F0
PCD2.M150	0F0
PCD2.M170	0F0
PCS1	0F0