F08700 — CAN: Communications error

F08700 is raised when the drive detects a CAN communications error on the connection to the higher-level control system. The manual splits the condition into two cases, which the fault value in r0949 (interpreted as a decimal number) tells apart: a send-telegram error counter that has run past the BUS OFF limit, and node life time monitoring that has expired. Depending on the drive's configuration, the same condition can also be issued as an alarm instead of a fault.

• Fault value 1 — BUS OFF: the error counter for the send telegrams has exceeded the BUS OFF value 255, and the bus has disabled the CAN controller. The manual names a bus cable short circuit, an incorrect baud rate and incorrect bit timing as causes.
• Fault value 2 — life time expired: the master no longer interrogated the CAN node status within its “life time”, obtained from the guard time (p8604[0]) multiplied by the life time factor (p8604[1]). The manual names an interrupted bus cable, a bus cable that is not connected, an incorrect baud rate, incorrect bit timing and a master fault as causes.

1. Check the bus cable — fault value 1 points to a short circuit, fault value 2 to an interruption or a missing connection.
2. Check the baud rate (p8622); an incorrect baud rate is listed for both fault values.
3. Check the bit timing (p8623).
4. Check the master — on fault value 2 it may itself be the faulty partner.
5. Once the cause has been resolved, remember the manual's explicit requirement: The CAN controller must be manually restarted with p8608 = 1 after the cause of the fault has been resolved!

• The drive writes the fault value into r0949; interpret it as a decimal number.
• 1 — the error counter for the send telegrams has exceeded the BUS OFF value 255; the bus disables the CAN controller.
• 2 — the master has not interrogated the CAN node status for longer than its “life time”, obtained from the guard time (p8604[0]) multiplied by the life time factor (p8604[1]).

• r0949 — read the fault value here, interpreted as a decimal number, to tell a BUS OFF condition (1) from an expired life time (2).
• p8604 — CAN life guarding: guard time [0] multiplied by life time factor [1] gives the life time within which the master must interrogate the node (fault value 2).
• p8622 — check here whether the set CAN bit rate matches the rest of the bus.
• p8623 — check here whether the selected CAN bit timing is correct.
• p8608 — set to 1 after the cause is resolved to clear the BUS OFF error and restart the CAN controller manually.
• p8641 — use it to set the fault response to this CAN error as required.

Acknowledge the fault immediately; the drive only returns to a ready state once this is done. Resolving the cause alone is not enough: the manual requires that the CAN controller be restarted manually with p8608 = 1 after the cause of the fault has been resolved. The same condition can also appear as an alarm, depending on how the drive is configured.