ModBus Mode Communications
Append
ix
B
B–22
Message Config-
uration: Query
Each frame is formatted as follows:
Slave address:
• This is a numer from 1 to 32 assigned to each inverter (slave). (Only the inverter having the
address given as a slave address in the query can receive the query.)
• When slave address “0” is specified, the query can be addressed to all inverter simultane-
ously (broadcasting).
• In broadcasting, the host (master) cannot read inverter data nor perform a loopback test.
Data:
• The data contains a function command.
• The data format used in the SJ700
2
corresponds to the ModBus data format below.
Function Code:
Specify a function you want to make the inverter execute. Function codes available to the
SJ700
2
are listed below.
Error check:
Modbus-RTU uses CRC (Cyclic Redundancy Check) for error checking.
• The CRC code is 16-bit data that is generated for 8-bit blocks of arbitrary length.
• The CRC code is generated by a generator polynomial CRC-16 (X
16
+ X
15
+ X
2
+ 1).
Frame Format
Header (silent interval)
Slave address
Function code
Data
Error check code
Trailer (silent interval)
Name of Data
Description
Coil
Binary data that can be referenced and changed (1 bit long)
Holding Register
16-bit data that can be referenced and changed
Function
Code
Function
Maximum data size
(bytes available per
message)
Maximum number of
data elements per
message
01h
Read Coil Status
4
32 coils (in bits)
03h
Read Holding Register
8
4 registers (in bytes)
05h
Write in Coil
2
1 coil (in bits)
06h
Write in Holding Register
2
1 register (in bytes)
08h
Loopback Test
—
—
0Fh
Write in Coils
4
32 coils (in bits)
10h
Write in Registers
4
4 registers (in bytes)
