PEAK-System Forum

Hi Guys,

I'm trying to find a bit more information out with regards to the MicroMod and how it behaves in response to a RTR message in particular, although the question may be applicable to all messages transmitted by a MicroMod.

In the event of a message collision, is there a limit to how many attempts a MicroMod will reattempt to transmit a failed response? Alternatively in the event of repeated failed attempts, do MicroMods time-out after a set period and simply cease all further attempts?

In other words, is it possible for a MicroMod to NOT respond to a RTR message?

I've tried looking on the PEAK forums and in the documentation, but cannot find any detail into the MicroMod behavior under these (hopefully rare) circumstances.

Thanks,

Mark

Hello Mark,

RTR-Messages are received and processed by the CPU. There is no automatic message created by the CAN-Controller in case a RTR-Message is received.
Data-Frames and RTR-Frames with the same CAN-Identifier do not produce a colission in case they are transmitted at the same time, because a data-frame has a higher priority and the node that transmits the RTR-frame stops sending the rtr-frame.
A collision can only occur if two different nodes send the same CAN-Identifier and the same frame type (data or rtr) at the same time. This case should be avoided.
If after the arbitration field more than one node is still transmitting and one of the following databits of both nodes are different, the node that transmitted the "1" will see a bit error ("0" is dominant and overrides a "1"), create an error frame and destroys the current can frame. In case of an error frame can-controllers increment their internal error-counter and try to retransmit the can-frame. If the collision persists and the error-counter reaches 255 the can-controller bus-state changes to "bus-off". Now it depends on the firmware whether the can-controller stays bus-off or automatically restarts. PCAN-Micromod firmware automatically restarts.

Regards,
Gunnar Bohlen