Special requirements with CAN

CAN is a message-oriented bus system. In addition to the data frame, it therefore requires identifiers that uniquely identify each message The modules support the standard 11-bit identifier. The low 8 bits are thereby used for the unique module ID => up to 255 different modules can be addressed. The remaining unassigned 3 bits are encoded as follows:

• 0x03 Error signal from module
• 0x05 Message from master to a module
• 0x07 Response from module
  

The other statuses are not used.

• A message sent to the module thus contains the following identifier: 0x5XX. (XX module address in hex format).
• A message sent by the module contains the following identifier: 0x7XX. (XX module address in hex format)
• In the event of an error, the messages from the module to the master are equipped with the identifier: 0x3XX. (XX module address in hex format)
  

At most 8 data bytes can be sent with a CAN message. Under certain circumstances, it might be necessary to combine several CAN messages in a longer data frame (D-Len > 7). This can be done with the fragmentation protocol.

Fragmentation is normally not necessary, as all commands required for the proper operation of the modules can be encoded in single CAN messages.