304 • Application examples
Modular I/O System
ETHERNET TCP/IP
Example of the MODBUS function code
In the case of SCADA Software Lookout from National Instruments the
MODBUS function codes are used with a 6 bit coding, whereby the first bit
represents the function code:
Input code:
MODBUS function code
0
FC1
Ø
read coils
Reading of several input bits
1
FC2
Ø
read input discretes
Reading of several input bits
3
FC3
Ø
read multiple registers
Reading of several input registers
4
FC4
Ø
read input registers
Reading of an individual input register
The following five digits specify the channel number of the consecutively
numbered digital or analog input and/or output channels.
Examples:
-
Read the first digital input:
i.e. 0 0000 1
-
Read the second analog input:
i.e. 3 0000 2
Application example:
Thus, the digital input channel 2 of the above node "Measuring data" can be
read out with the input: "Measuring data. 0 0000 2".
Fig. 7-1: Example of user software
G012913e
i
More information
Please refer to the respective SCADA product manual for a detailed description
of the particular software operation.