CAN Repeater Inhibit Time

Inhibit time for EMS CAN repeaters

Our CAN repeaters are shipped with a preset blocking time. It is important to select the correct blocking time for the required baud rate to ensure that the repeater functions properly in the target system. We recommend setting the hold time to 10–20% of the bit time. In the case of CAN-FD-capable CAN repeaters, the Classic CAN baud rate used during the arbitration phase is decisive, not the flexible (faster) data rate of the message transmission. The technical background remains unchanged and will be explained here.

If the CAN signal goes from recessive to dominant on one side of the repeater it is propagated to the other side and here the signal also changes to dominant. If the first signal goes back to recessive, there is still a dominant level on the other side, it is hold dominant by the capacitance of the cable. In this moment the repeater cannot decide, if this dominant signal on the second side is the old signal and will fade out or if it is a new signal originated by a node on the second side and should be propagated. This effect can occur e.g. during the arbitration phase of the CAN protocol. The consequence is that at this moment for a short period of time a back transmission of the dominant signal has to be omitted.

The following table should give an overview about commonly used values: