Filter
Top Products
User Manual MON20/20 Software for Gas Chromatographs
3-9000-745 SEPTEMBER 2010
7-2
This section provides detailed instructions for using the Modbus program.
Use this program only if you are familiar with Modbus communication
protocol and the operation of MON 20/20.
7.1.1 Comparing Modbus protocols
MON 20/20 and the Modbus program can accommodate two different
Modbus protocols: SIM_2251 and User_Modbus. Separate Modbus
registers are reserved for each protocol; therefore, some settings for MON
20/20 and WinMB depend on which Modbus protocol is used.
The protocol you need depends, ultimately, on the hardware used for data
acquisition from the GC Modbus register contents.
The following comparison should help clarify the differences between the
two protocols as well as the utility of each.
Table 7-1. Comparing SIM_2251 and User_Modbus Protocols
SIM_2251 User_Modbus
Serial slave port Serial slave port
Modified protocol that allows floating point
numbers to be transmitted over Modbus via 2251
emulation slave type
Standard Gould protocol that accommodates PLC
Emulation LO-HI (PLC-LH)
Most register contents are predefined; some
registers can be user-defined
Predefined Boolean (coils)
User-defined Numeric (registers)
Data types are predefined for registers 1000 to
9000
Data types are user-defined
Variables assigned to registers can be listed in the
GC Config Report. For instructions and an
example report, see Section 5.12. See Appendix C
for more detail about individual registers.
Variables assigned to registers can be listed in the
GC Config Report. For instructions and an
example report, see Section 5.12. See Appendix C
for more detail about individual registers.
When using the Modbus program, set Register
Mode to “DANIEL” to view register contents.
When using the Modbus program, set Register
Mode to “PLC- LH” or “PLC-HL” to view register
contents.
It is not necessary to assign scales to registers. It may be necessary to assign scales to registers, to
convert floating point values to whole integer
representations.