Unlike Modbus serial link, Modbus TCP/IP is not based on a hierarchical structure, but on a client/server model.
The TM4ES4 module implements both client and server services so that it can initiate communications to other controllers and I/O devices, and to respond to requests from other controllers, SCADA, HMIs and other devices. By default, Modbus Server functionality is not active.
Without any configuration, the TM4ES4 module supports Modbus server.
The Modbus Server/Client is included in the firmware, and does not require any programming action from the user. Due to this feature, it is accessible in RUNNING, STOPPED and EMPTY states.
The Modbus TCP client supports the following function blocks from the PLCCommunication library without any configuration:
oADDM
oREAD_VAR
oSEND_RECV_MSG
oSINGLE_WRITE
oWRITE_READ_VAR
oWRITE_VAR
For further information, refer to the Function Block Descriptions.
The Modbus server supports the following Modbus requests:
|
Function Code Dec (Hex) |
Sub-function Dec (Hex) |
Function |
|---|---|---|
|
1 (1h) |
|
Read digital outputs (%Q) |
|
2 (2h) |
|
Read digital inputs (%I) |
|
3 (3h) |
|
Read holding register (%MW) |
|
6 (6h) |
|
Write single register (%MW) |
|
8 (8h) |
|
Diagnostic |
|
15 (Fh) |
|
Write multiple digital outputs (%Q) |
|
16 (10h) |
|
Write multiple registers (%MW) |
|
23 (17h) |
|
Read/write multiple registers (%MW) |
|
43 (2Bh) |
14 (Eh) |
Read device identification |
The table contains the Data Selection Code list:
|
Data Selection Code |
Description |
|---|---|
|
0x00 |
Reserved |
|
0x01 |
Basic Network Diagnostics |
|
0x02 |
Ethernet Port Diagnostic |
|
0x03 |
Modbus TCP/Port 502 Diagnostics |
|
0x04 |
Modbus TCP/Port 502 Connection Table |
|
0x05 - 0x7E |
Reserved for other public codes |
|
0x7F |
Data Structure Offsets |
