Ulvac MBD-D - Page 22

10 ULVAC CRYOGENICS INCORPORATED
 Function Code: This code tells what kind of action to perform. Functions to read and write
can be specified.
Function Code Function Data Type Notes
0x03
Continuous
reading
16Bit Word
Temperature and
conditions
0x10 Continuous 16Bit Word Parameter
 Data: Data differs by function code.
If continuous reading is selected, the data comprises Register Address of the device where
reading starts and the number of Registers to read. If continuous writing is selected, the
data comprises Register Address of the device where writing starts, and the number of
Registers to write continuously.
 Error Check (CRC): Checks the validity of the contents to communicate. IF the device is
in communication and is experiencing entanglement or disconnection, such communication
is regarded as invalid. The MBD-D performs Error Check following the CRC-16 method.
The CRC-16 calculation is as follows;
The data to send is divided by generator polynominal to work out the remainder.
generator polynominal：X
16
+X
15
+X
2
+1
For detailed information on CRC calculation, refer to Modbus web site at Modbus.org.
 Examples of Modbus Communication Protocol
<Continuous reading (0x indicates hexadecimal) example>
Request message from the master
Byte (8)
Response message from the Slave(MBD-D)
Byte (9)
The above example is of the message of continuous reading of two registers from MBD-D
register address of 104(0x68).
Address
Function
Code
Register Address
Number of
Registers
Error Check
0x68 0x03 0x0002 0x0002 0x6CF2
1 1 2 2 2
Address
Function
Code
Response Byte
number
Data Error Check
0x68 0x03 0x04 0x0B930B81 0x6CF2
1 1 1 4 2