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Multiple messages have to be transferred by CAN Pack/Unpack

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Saeed Soltani
Saeed Soltani am 7 Jul. 2016
Kommentiert: Walter Roberson am 11 Aug. 2022
If we have several messages to be sent, is there any possibility to set multiple messages on one CAN Pack/Unpack or the only way is to use several modules (for each message one)?

Antworten (1)

Dimitri MANKOV
Dimitri MANKOV am 11 Aug. 2022
Hi Saeed,
As far as I know, you should use one CAN Pack/Unpack block per CAN Message ID.
I hope this is helpful!
  1 Kommentar
Walter Roberson
Walter Roberson am 11 Aug. 2022
... well, you could in theory use your 64 bits of payload to pack additional messages, if they somehow fit within the 64 bits. However, you should not expect the receiving systems to be able to look inside the payload to recognize the additional packed messages. The CAN messages do not contain information about the meaning of or internal field lengths of the payload.
If, somehow, the information about the length of each sub-field was transmitted with the block, then the amount of memory requried to store the maximum subfield length would be 5 bits (length 0 is not meaningful, so encode (bitlength - 1)). There could be up to 64 fields, each of length 1. The naive storage requirement for such a description would then take 64 * 5 = 320 bits. You would have to start using data compression techniques to pack the length fields; you could definitely need at least 64 bits for the field lengths alone.... In other words, it would not be practical.

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