E6582051
- 60 -
8. Modbus TCP
8.1. Header format
Byte Description Comments
0
Transaction
identifier
high order Same transaction ID is returned from Modbus TCP server.
Fixed at 0 if it is not required.
1 low order
2
Protocol
identifier
high order
This identifier always equals 0.
3 low order
4
Length of data
high order Number of bytes after the Unit ID (Byte 6). The value of the high
order should be “0”, because the frame length is always less
than 256 bytes.
5 low order
6 Unit ID (Destination identifier) Chose from Unit ID described in Section 8.2.
7 Modbus request function code Chose from Function code described in Section 8.3.
8.2. Setting of Unit ID
The Unit ID (destination identifier) is used to access inverter Modbus TCP servers:
Unit ID Modbus TCP server Accessible data
0-248 Inverter (VF-S15/AS3/MB1) Inverter parameter
Device identification of inverter
251 Communication module
(this product)
Device identifications of module
8.3. List of Modbus functions supported
Function code Function name Description Size of data
03 (0x03) Read Holding Register Read N output words 63 words max.
06 (0x06) Write Single Register Write one output word -
16 (0x10) Write Multiple Registers Write N output words 63 words max.
43 (0x2B) Read Device Identification Identification -
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