Modbus Integrator's Guide for the CXC HP | 2 - Using Modbus
2.3. Modbus Data
There are two types of data available over Modbus: limited data set and a full system data set for the DC
system and each AMPS HP system.
2.3.1. Limited Data Set
The Limited Data Set has a small number of DC system related parameters. This data set uses only the
input registers table (04). The default Device ID is 247. For a list of available data refer to the Limited
Data Set Data Points section.
2.3.2. Full System Data Set
A full system data set is available for the DC system and each AMPS HP system. This data set has all
parameters related to the system as well as other data such as custom, data, timers, counters and ADIO
readings. Three Modbus registers are used: coils status(01), input status (02), input register (04). The
default device id is 1.
The structure of a full system data set is much different than for the Limited Data Set. When working with
the controller, it is possible to create and remove inventory to match a physical system, or to create and
remove things like user alarms, custom data, timers and counters. Because of this dynamic nature there
are limits to the number of item that can be assigned Modbus addresses.
The data available for each device ID always includes controller data. The following tables show the types
of data contained in the Modbus table, the starting address for each type of data, and the limitation to the
number of data supported. Note that system data always starts at address 5001.
Table 2. Modbus Address Allocation for Common Controller Data
Source Maximum Number
of Source Items
Start of Coil Status
Register (01)
Start of Input Status
Register (02)
Start of Values Reg-
ister (04)
Controller 1 1 10001 30001
Custom Data 128 203 10203 30203
Timers 128 717 10717 30717
Counters 128 1231 11231 31231
User alarms 64 1745 11745 31745
reserved 1 2003 12003 32003
ADIO 24 3541 13541 33541
Table 3. Modbus Address Allocation for DC System Data
Source Maximum Number
of Source Items
Start of Coil Status
Register (01)
Start of Input Status
Register (02)
Start of Values Reg-
ister (04)
DC System 1 5001 15001 35001
0350114-J0 Rev G Page 11
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