The ClearSCADA Advanced Modbus Driver supports several Modbus function codes, enabling it to read and write data on Modbus devices. The standard function codes that the ClearSCADA Advanced Modbus Driver supports are:
| Modbus Function Code | Functionality | Maximum Number of Registers that can be Read or Written to using a Single Command |
|---|---|---|
|
FC1 |
Read Coil Status |
2000 |
|
FC2 |
Read Input Discretes |
2000 |
|
FC3 |
Read Multiple Registers |
125 |
|
FC4 |
Read Input Registers |
125 |
|
FC5 |
Write Single Coil |
1 |
|
FC6 |
Write Single Register |
1 |
|
FC15 |
Write Multiple Coils |
3 |
|
FC16 |
Write Multiple Registers |
4 |
|
FC22 |
Mask Write Register |
1 |
NOTE: The actual maximum number of registers or coils requested in a read might be smaller than the number listed above. This will occur if a channel’s Maximum Packet Size has been reduced (see Specify the Required Modbus Protocol and Packet Size).
As only a limited number of Modbus controllers support FC22, this function is made optional on Generic Modbus Digital Output Points in ClearSCADA (see Specify the Type of Control Operation).
Similarly, as some Modbus controllers do not support both FC6 and FC16, each generic controller’s Register Write function has to be specified in ClearSCADA (see Specify the Register Write Function).