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ANNEX I CU.K. Requirements for construction, testing, installation, and inspection
Appendix 7
DATA DOWNLOADING PROTOCOLS U.K.
2.V.U. DATA DOWNLOADINGU.K.
2.2. Data download protocol U.K.
2.2.5 Error handling U.K.
If an error occurs during the message exchange, the message flow scheme is modified depending on which equipment has detected the error and on the message generating the error.
In figure 2 and figure 3 the error handling procedures for the VU and the IDE are respectively shown.
2.2.5.1 Start Communication phase U.K.
DDP_020If the IDE detects an error during the Start Communication phase, either by timing or by the bit stream, then it will wait for a period P3 min before issuing again the request.U.K.
DDP_021If the VU detects an error in the sequence coming from the IDE, it shall send no response and wait for another Start Communication Request message within a period P3 max.U.K.
2.2.5.2 Communication phase U.K.
Two different error handling areas can be defined:
The VU detects an IDE transmission error.
For every received message the VU shall detect timing errors, byte format errors (e.g. start and stop bit violations) and frame errors (wrong number of bytes received, wrong checksum byte).
If the VU detects one of the above errors, then it sends no response and ignores the message received.
The VU may detect other errors in the format or content of the received message (e.g. message not supported) even if the message satisfies the length and checksum requirements; in such a case, the VU shall respond to the IDE with a Negative Response message specifying the nature of the error.
The IDE detects a VU transmission error.
For every received message the IDE shall detect timing errors, byte format errors (e.g. start and stop bit violations) and frame errors (wrong number of bytes received, wrong checksum byte).
The IDE shall detect sequence errors, e.g. incorrect sub message counter increments in successive received messages.
If the IDE detects an error or there was no response from the VU within a P2 max period, the request message will be sent again for a maximum of three transmissions in total. For the purposes of this error detection a sub message acknowledge will be considered as a request to the VU.
The IDE shall wait at least for a period of P3 min before beginning each transmission; the wait period shall be measured from the last calculated occurrence of a stop bit after the error was detected.
