Data Transfer and PDO Assignment
CAN-CBX-COM2
Manual • Doc.-No.: C.3055.21 / Rev. 1.1
Page 91 of 125
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8.10 Data Transfer and PDO Assignment
8.10.1 Function Description of local Firmware
Serial data is buffered between CAN and serial interfaces in both directions via a 256 byte sized ring
buffer. The data which is received first is transmitted again first (FIFO).
If the ring buffer is full and further data is received, this data will be lost. Therefore, the transmission
rates of CAN and the serial interfaces have to be synchronized.
8.10.1.1 Data Transfer CAN -> Serial Interface
The number of CAN data which is to be stored in the ring buffer within an interval has to be smaller
than the number of data transmitted via the serial interface, because otherwise the ring buffer might
overflow.
The number of data received per interval depends on the number of data bytes transmitted, the
frequency of transmissions, the bit rate of the CAN, and the degree of CAN bus utilisation.
If data is lost during operation, breaks between transmissions have to be extended and/or the number
of bytes transmitted has to be reduced.
The data is transmitted from CAN via identifier RPDO1 to the module. Up to 8 bytes ca be selected to
be transmitted.
The data transfer from CAN to serial interface has the following chronological course:
Fig. 24: Data transfer CAN -> serial interface (parameter TxMinCharStart = 0)
In addition, the CAN-CBM-COM2 module offers an RTR handshake at which the module informs the
CAN partner via RTR, that the local ring buffer still can receive data. No data are sent any more if the
ring buffer is full (see page 106).