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5. MODBUS-RTU protocol
The MODBUS-RTU protocol of VF-S11 supports only part of the MODBUS-RTU protocol. Only two
commands are supported, “03: Multiple data read (limited only to two bytes)” and “06: Word writes.”
All data will be binary codes.
■ Parameter Setting
• Protocol Selection ()
Select “MODBUS－RTU protocol ( = ) in the communication selection parameters. “TO-
SHIBA Inverter Protocol” (=) is set for communication protocol selection in initial shipment
setting. (See “3. Communication protocol.”)
* Caution when selecting MODBUS-RTU protocol
The extension panel (RKP001Z) and parameter writer (PWU001Z) , these options cannot be used.
Note that Parameter Numbers. , , , and to do not
function.
• Inverter Number (
Inverter numbers. 0 to 247 can be specified in MODBUS-RTU. “0” is allocated to broadcast com-
munication (no return). Set between 1 and 247.
<Related Parameter: Change and set as necessary>
: Communication baud rate
: Parity
: Communication error trip time
■ Timing of Message from Host
MODBUS-RTU sends and receives binary data without a frame synchronization header character
and defines the frame synchronizing system to recognize the start of a frame by no-data time.
MODBUS-RTU initializes frame information and decides the data that is first received subsequently
as the first byte of a frame if data is not communicated within a time for 3.5 bytes, including the start
and stop bits, at the transmission speed of the on-going communication while standing by for data
reception. If a frame is being received before no-data time for 3.5 bytes, this frame will be aborted.
Be sure to provide more than 3.5 bytes for data send interval.
Send data so that the time between characters will not be spaced for more than 1.5 bytes. Other-
wise, MODBUS-RTU will sometimes recognize it as a start of data.
In the case of data to other stations, messages from the host and responses from other stations are
also received. A wait time for 3.5 bytes is needed before starting transmission after own station
completes reception when sending a response to recognize a frame start at this time.