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Appendix C, Modbus registers list
There are two GC Modbus registers that may be of interest to the
developer: SIM_2251 and User_Modbus. Differences betweeb the two
registers are summarized in Table C-1.
C.1 User_Modbus register list
Table C-2 lists only variables included in the User_Modbus Boolean
Modbus registers. These registers are not user-defined and primarily
contain alarm flags that may be useful for debugging purposes. To use the
Modbus program to view the contents of these registers, you will need to
set the Function parameter to 1 (Read Coil). See Section 7.1 for details
on using the Modbus program.
All other User_Modbus registers can be defined by the user. To define
User_Modbus register contents, see Section 4.12.3.
Table C-1 Comparison of SIM_2251 and User_Modbus
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.
The standard Gould Modbus protocol that
accommodates PLC Emulation LO-HI.
Nearly all register contents are predefined; a few
9000-series registers can be user-defined (i.e.,
read-write).
Boolean (coils) are predefined. Numeric
(registers) 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.
Variables assigned to registers can be listed in
the GC Config Report. For instructions and an
example report, see Section 5.12.
When using the Modbus Test program, set
Register Mode to “DANIEL” to view register
contents (see Section 7.1.2).
When using the Modbus Test software, set
Register Mode to “PLC LH” to view register
contents (see Section 7.1.2).