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5. MODBUS-RTU protocol
The MODBUS-RTU protocol of VF-AS1 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 (
,
=
) in the communication selection parameters.
“TOSHIBA” (
,
=
) is set for communication protocol selection in initial shipment set-
ting. (See “3. Communication protocol.”)
* Caution when selecting MODBUS-RTU
Note that selecting this protocol disables the inter-drive communication functions set with parame-
ters
and
, and the block communication functions set with parameters
,
and
to
.
•
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>
: Baud rate (2-wire RS485)
: Communication speed (4-wire RS485)
: Parity (common to 2-wire RS485 and 4-wire RS485)
Data Exchange with Inverters
The inverters are always ready to receive messages and perform slave operation in response to
computer requests.
A transmission error will result if the transmission format does not match. The inverters will not re-
spond if a framing error, parity error, CRC error or an inverter number mismatch occurs. If no re-
sponse is received, the computer side recognizes that a communication error has occurred.
Transmit data again.
(1) In case spacing for more than 3.5 bytes are provided before characters, all data immediately
preceding it will be aborted. Data will sometimes be aborted if spacing for 1.5 bytes or more is
provided between characters. (See “3.1. About the handling of received frames.”)
(2) Communication will be effective only when inverter numbers match or the communication mode
is 0 (Broadcast communication). If there is no inverter number that matches or 0 (broadcast
communication) is specified, no response is returned by any inverter.
(3) Message reception will end if spacing for more than 3.5 bytes are provided at the end of charac-
ters. (See “3.1. About the handling of received frames.”)
(4) If no communication take place within the time specified using the timer function, the computer
will assume that a communication error has occurred and trip the inverter. The timer function is
disabled when the inverter is turned on or initialized. For details, see Section 7.3, “Timer function,
Communication time-out time action.”
(5) On executing the command received, the inverter returns data to the computer. For the response
time, see Appendix 2, “Response time.”
Caution:
Communication is not possible for about two seconds after the power is supplied to the inverter until
the initial setting is completed. If the control power is shut down due to an instantaneous voltage
drop, communication is temporarily interrupted.
