Fuji Electric FRENIC-VG Series, User Manual

Page: 33 / 346

5.1 Standard RS-485 Communications Ports
5-13
Chap. 5
USING ST
ANDARD RS-
485
5.1.8 Host side procedures
Please follow the flow chart for each frame transmission procedure.
For both reading and writing, always confirm the response before sending the next frame. If there is
no response from the inverter after a certain time, execute a timeout and retry. (If you attempt to start
a retry before a timeout, the request frame will not be received properly.)
Retry
When executing a retry, either use a standard frame to resend the data that was sent before no
response was received or execute polling (M26) to enable the error details to be read, and then check
that the response was normal. (When checking the response, you will need to determine whether a
further timeout is necessary.)
If the response is normal, this indicates that some kind of temporary transmission error such as noise
occurred, and normal communications should be possible thereafter. (If there is frequent
reoccurrence of this phenomenon, it is necessary to investigate further to determine whether there is
an error.)
If there is again no response, execute further retries. If the number of retries exceeds the preset value
(normally about 3 times), there may be a problem with the hardware or the software of an upper
level device. As there is no response from the specified station, it will be necessary to abort and
investigate further.
5.1.8.1 Read procedure
Start
Request frame sent
Response frame received?
Normal (ACK) response?
Normal finish
Transmission error detected
Format error?
Command error?
Function code error?
Change to correct format and
resend.
Abort
Change to correct command and
resend.
Change to correct function code
and resend.
Yes
No
No
Yes
Yes
Yes
Yes
No
No
No