CM578-CN CANopen® Communication Module CAN Queues

The several received CAN identifiers with their message contents are assigned to their different input buffers (Nodeguard input queue, Management input queue, emergency input queue).

A received message is interpreted directly after it has been received from the CAN Controller. This message will be transferred to the corresponding queue while they are written to the output buffer, if the CAN chip is just sending a message. A main loop is interpreting these messages and deletes them or the Interrupt Handler sends the next message. The input buffer handler has 3 parameters. Their content are displayed by Automation Builder.

bInner is the number of currently saved messages.

bFront is a pointer where the next message will be saved.

bRear is a pointer where the next message will be deleted from the queue body.

In a running system, the value of bInner normally should decrease to 0 and bFront and bRear should have equal values.

Parameter	Description
bRear	Position of the next read access to the puffer of received CAN telegrams
bFront	Position of the next write access
bInner	Number of CAN telegrams which are actual included in the buffer