Hitachi SJ700-2 instruction manual Communication in Modbus-RTU mode

Chapter 4 Explanation of Functions

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:

(1) (1)

External control system

Inverter

(2)

Time

Waiting time (silent interval + communication wait time [C078])

(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].)

(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	Function code	Range of data	Description
		00: Tripping	The inverter trips (E41) after reception
			timeout.
		01: Tripping after	The inverter decelerates and stops the
			motor, and then trips (E41) after reception
		stopping the motor
			timeout.
Selection of operation	C076	02: Ignoring the errors	The inverter ignores the error without tripping
			and alarm output.
after communication error
		03: Stopping the	The inverter stops the motor after
		motor after	free-running without tripping and alarm
		free-running (FRS)	output after reception timeout.
		04: Decelerating and	The inverter decelerates and stops the motor
			without tripping and alarm output after
		stopping the motor
			reception timeout.
Communication trip limit	C077	0.00 to 99.99 (s)	Limit time to determine the reception timeout
time setting
			Time to wait until the inverter starts sending a
Communication wait time	C078	0. to 1000. (ms)	response after reception of a query
			(excluding the silent interval)

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.

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