Communication In Modbus-Rtu Mode - Hitachi SJ700-2 Instruction Manual

4.4.2 Communication in Modbus-RTU mode

(1) Communication protocol
The communication between the inverter (slave) and external control system (master) is based on the
following protocol:
External control system
Inverter
(1): Query frame that is sent from the external control system to the inverter
(2): Response frame that is sent from the inverter to the external control system
(3): Communication trip limit time (C077)
If the inverter cannot complete the reception of a query from the master system (external control
system) within the communication trip limit time, after having sent a response to the preceding query,
the inverter enters the status in which to receive the query from the beginning. Subsequently, the
inverter returns no response to the master system.
After reception timeout occurs, the inverter operates according to the setting of the selection of
operation after communication error (C076). For details, see the table below. Monitoring of reception
timeout begins when the first communication is performed after the inverter power has been turned
on or the inverter has been reset. Reception timeout is monitored only when the inverter
communicates with the master system.
Item
Selection of operation
after communication error
Communication trip limit
time setting
Communication wait time
The inverter sends a response (frame (2)) always after receiving a query (frame (1)). The inverter does
not actively output any frame to the external control system.
(1)
Waiting time (silent interval +
communication wait time [C078])
Function code Range of data
00: Tripping
01: Tripping after
stopping the motor
02: Ignoring the errors
C076
03: Stopping the
motor after free-
running (FRS)
04: Decelerating and
stopping the motor
C077 0.00 to 99.99 (s)
C078 0. to 1000. (ms)
Chapter 4 Explanation of Functions
(2)
(3) Communication trip limit time (C077)
(If reception timeout occurs, the inverter will
operate according to the setting of the
operation selection after communication
error [C076].)
The inverter trips (E41) after reception
timeout.
The inverter decelerates and stops the
motor, and then trips (E41) after reception
timeout.
The inverter ignores the error without
tripping and alarm output.
The inverter stops the motor after free-
running without tripping and alarm output
after reception timeout.
The inverter decelerates and stops the
motor without tripping and alarm output after
reception timeout.
Limit time to determine the reception timeout
Time to wait until the inverter starts sending
a response after reception of a query
(excluding the silent interval)
4 - 132
(1)
Time
Description