8 (32)
3.4.1
Modbus Points Definition
Each point defined in the gateway has the following Modbus features associated to it:
Feature
Description
Modbus Device
Modbus TCP device to which belongs the point, from a list of Modbus TCP slave devices
that can be defined in the gateway (up to 5).
For every Modbus TCP slave device defined, a virtual signal is created automatically in
the gateway to inform about the communication with the device, this signal is available
also from the KNX interface like the rest of the points.
Function code
Read Func
Write Func
One of the following Modbus function codes can be used:
•
1- Read Coils.
•
2- Read Discrete Inputs.
•
3- Read Holding Registers.
•
4- Read Input Registers.
•
5- Write Single Coil.
•
6- Write Single Register.
•
15- Write Multiple Coils.
•
16- Write Multiple Registers.
#Bits
Number of bits to be used by this signal.
Data Coding Format
One of the following Modbus data coding formats can be used:
•
16/32/48/64 bits unsigned.
•
16/32/48/64 bits signed (one’s complement – C1).
•
16/32/48/64 bits signed (two’s complement – C2).
•
16/32/48/64 bits Float.
•
16/32/48/64 bits Bitfields.
•
Error comm
Byte Order
•
Big Endian
•
Little Endian
•
Word Inverted Big Endian
•
Word Inverted Little Endian
Register Address
The Modbus register address inside the slave device for the point.
Bit inside the register
Bit inside the Modbus register (optional). The gateway allows bit decoding from generic
16 bits input/holding Modbus registers.
Bit coding into 16 bit input/holding Modbus registers is used for some devices to encode
digital values into this type of registers, being these registers normally accessible using
Modbus function codes 3 and 4 (read holding/input registers).
Modbus to KNX Gateway User Manual
SCM-1202-050 1.2 en-US
