IMO VXSM75-1 Instruction Manual page 96

(3) Transmission procedure
1) Set communication functions H30 through
H39.
2) Make communication
transmission frames.
3) If no response returns for one second from
the inverter upon a frame from the host, retry
communication. Several retries indicate
certain errors. Make investigation.
4) If no communication is received from the host
for 30 seconds after the first operation
command is received, the inverter judges a
transmission breakdown error and shuts
down the inverter output, leaving the motor to
coast to stop.
5) After consecutive eight communication
errors, the inverter output is shut down and
the motor coasts to stop.
(4)Host controller transmission procedure
Do not send the next frame unless the response
is returned.
If the inverter does not respond for longer than
the standard time, timeout should be judged and
retry should be performed. If a retry is started
Specifications
before timeout, normal reception may become
impossible, so that timeout should be judged
correctly. The timeout time is one second in the
selecting mode and 0.5 second in the polling
according to
mode. In the retry sequence, send the same
frame again as that sent before no response, or
send a polling (M26: communication error
monitor) frame for reading an error, and check
for a normal response. (Judge the timeout again
during the check.)
If a normal response is returned, a transient
transmission error due to noise or the like is
indicated, and correct communication can be
continued. If retries occur frequently, any
abnormalities
investigation is necessary. If no response is
returned, continue retrying. If there are three
retries, there is some trouble in the hardware or
software of the host controller. Terminate the
software of the host controller and investigate.
No error code is returned in the case of negative
acknowledgment of a short frame. Judge the
error code using the communication error
monitor (M26) separately.
are probable. In-depth
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