Instruction Manual

Rev 2.0 : X11CA-IM MASTER MODULE

4 MODBUS COMMUNICATION PROTOCOL

4.1 Slave Address Setting

The Slave Address switch (SW1 or SW3, depending on the revision of the PCB) on

the X11CA-IM Module sets the Slave Address of the X11CA-IM Master Module

for MODBUS RTU communication as shown below.

Slave

address

SW1-1 SW1-2 SW1-3 SW1-4

1 OFF OFF OFF OFF

2 ON OFF OFF OFF

3 OFF ON OFF OFF

4 ON ON OFF OFF

5 OFF OFF ON OFF

6 ON OFF ON OFF

7 OFF ON ON OFF

8 ON ON ON OFF

9 OFF OFF OFF ON

10 ON OFF OFF ON

11 OFF ON OFF ON

12 ON ON OFF ON

13 OFF OFF ON ON

14 ON OFF ON ON

15 OFF ON ON ON

16 ON ON ON ON

Table 4-1 Setting Modbus Slave Address

4.2 Data Communication Format

The data format for Modbus communication is 19200, no parity, 8 bit and 1 stop

bit.

4.3 Modbus RTU Protocol Function 3: Read the Holding Registers

To read the binary contents of the holding registers on the X11CA-IM from a host

device, use Modbus RTU Protocol function 3.

Query

The query message specifies the starting register and the quantity of registers

to be read. Registers are addressed starting at zero: registers 1-16 are addressed

as 0-15.