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User Manual MON20/20 Software for Gas Chromatographs
3-9000-745 SEPTEMBER 2010
7-6
2. Select the desired read or write option from the Function pull down
menu.
3. Type the starting register value in the Data Addr field.
Note
The data type is set automatically by the Modbus program, based on the specified data
address.
4. In the Quantity field, type the number of registers to be retrieved. The
Modbus program will accept a quantity value of 1 to 2016. The
requested number of registers cannot exceed the amount contained by
the selected message block but you can retrieve a partial block. You
cannot cross a message block boundary.
Also, in Standard Modbus mode each register is 16 bits. Therefore,
integers (SHORT) consist of 1 register while floats (FLOAT) and long
integers (
LONG) consist of 2 registers.
Note
Boolean registers are not user-defined (for either SIM_2251 or User_Modbus) and
primarily contain alarm flags useful for debugging. To view the contents of Boolean
registers, select the 1 (Read Coil) function code.
Numeric registers for User_Modbus can be user-defined. To view the contents of
Numeric registers, select the 3 (Read Regs) function code.
Function Code Description Broadcast
1 (Read Coil) Reads one or more coil values.
2 (Read Input Status) Reads one or more input status values.
3 (Read Multiple Regs) Reads one or more register values.
4 (Read Input Regs) Reads one or more input register values.
5 (Set Single Coil) set (write) one coil value
6 (Set Single Reg) set (write) one register value
15 (Set Multiple Coils) set (write) multiple coil values
16 (Set Multiple Regs) set (write) multiple register values