CHAPTER 13 RS-485 COMMUNICATIONS
13-34
Modbus RTU Communications
13
(4) Definition of amplifier’s timings
Timings on the amplifier side are defined as follows:
FC Information field T1 T2
T3
Recommended
timeout setting
Other
than
10h
-
Other than below
115200 bps：1.7 ms
38400 bps： 5 ms
19200 bps： 10 ms
9600 bps： 10 ms
100 ms
10h
Specify that n sets
of parameters or
positioning data are
written in
Within (n+2)×10 ms
115200 bps：1.7 ms
38400 bps： 5 ms
19200 bps： 10 ms
9600 bps： 10 ms
Same
as T1
250 ms
Response time
It is able to specify a response time of the amplifier (T1) by PA2_94 (response time).
However, actual response time becomes {time for 3 characters + time for executing processing} (T0)
or longer.
* Although T0 varies depending on communications baud rate, FC, and so on, the shortest time is 2.5
ms for 38,400 bps.
If any time longer than T0 is specified, the amplifier responses after waiting for the specified time.
After the master has sent a query, if it takes a long time until the master switches into the receiving state,
set PA2_94 (response time) as needed because responses from the amplifiers might not be received
correctly.
3. Error processing
Errors are classified into the following:
(a) Physical/character-level errors : Parity error, framing error, and so on
(b) Protocol level error (1) : CRC error
(c) Protocol level error (2) : Incorrect FC/address/data
Query
Response
Master ：
Amplifier：
Response
PA2-94 < T0
PA2-94 > T0 PA2-94
T0
PA2-94
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