User Manual

Modbus Interface Specifications
2
Modbus Data Model
13
Building Technologies
A6V10316242_a_en
CPS Fire Safety
31.05.2019
2.1.2 Modbus Functions
The gateway supports the following Modbus functions:
Function code
Function
Applicable table
types
Notes
0x02
Read Discrete Input
Bit Status
0x03
Read Holding
Registers
Command, Date and
Time
Use it for reading
date & time registers
0x04
Read Input Registers
Summary; Status;
Compact Status
Use it for reading
status information
0x06
Write Single Register
Command;
Synchronization
Use it for writing
command registers,
to perform control
actions, and date &
time registers, thus
synchronizing the
NK8237 clock.
0x07
Read Exception
Status
-
Serial Line only
0x08
Diagnostics
-
Serial Line only
0x0B
Get Comm Event
Counter
-
Serial Line only
0x11
Report Slave ID
-
Serial Line only
0x2B / 0x0E
Read Device ID
-
General NK8237
info.
2.2 Modbus Data Model
According to the Modbus protocol specifications, the application-level
communication between Modbus devices occurs via memory tables representing
the Modbus Registers . In fact, Modbus functions operate on registers to provide
both monitor and control I/O.
The gateway is capable of supporting an Input Register Map providing a process
image of the fire system status for the Modbus master/client stations, which
periodically read the input registers and acquire the related conditions. Control
actions can also be initiated by the Modbus master/client stations by writing
appropriate values in specific Holding Registers . This results then in command
messages being transmitted to the fire system.
2.2.1 Model Configuration Workflow
The detailed definition of the register map implementing the Modbus data model
occurs at configuration time. The Composer tool can import the
FS20/FS720/STT20 metafile (the object list) and create the register map that
represents the fire objects in a simplified set of types as described in the Register
Map [➙ 16] section.
The register map can be directly applied or further customized to adapt the
addressing scheme to your specific application. Some modifications to the map can
be done in the Composer configuration tool, including the tables’ base addresses
and individual offsets. In addition, any information of the map can be exported to a
CSV file , then customized externally, and finally re-imported to the Composer
environment.