Concept
RP-C Modbus
The RP controller Modbus RTU (RS-485) subnetwork allows standard Modbus devices and the KNX Modbus gateway (RP-C-EXT-KNX) to be connected to the controller. An adapter is required for converting the controller RS-485 Com port with RJ45 interface to screw terminals.
RP controller models with “-M” in the product name do not support the KNX Modbus gateway (RP-C-EXT-KNX).
The Modbus RTU protocol is used for the communication. The Modbus communications is characterized by communication between client device(s), which initiate communication and make requests of server device(s), which process requests and return an appropriate response. The RP controller acts as the Modbus client device and the connected (hosted) devices act as server devices.
For standard Modbus devices, a separate power supply unit (PSU) is needed to power the Modbus devices on the network.
For the KNX Modbus gateway, the RP controller provides both 24 VDC power supply and communications through the Modbus network connection.
It is recommended to use the Non-isolated RS-485 Adapter (SXWNISORS48510001) to provide screw termination of the Modbus device wiring and help avoid miswiring. The adapter converts an RS-485 RJ45 interface to screw terminals. For more information, see Non-isolated RS-485 Adapter .
For the KNX Modbus gateway, the RS-485 Power Adapter (SXWNISORS485P10001) can preferably be used to convert the RP controller RS-485 interface from RJ45 port to screw terminals because this adapter supports 24 VDC power supply from the controller to the KNX Modbus gateway. For more information, see RS-485 Power Adapter .
The maximum total length of the Modbus (RS-485) network is 72 m (236 ft).
The Modbus (RS-485) network cable should be routed in a continuous daisy-chain bus configuration without cable stubs. For more information, see Cable Routing .
Cable selection is important to achieve good performance and reliability of the Modbus (RS-485) network. The cable must provide twisted pairs and be specified for RS-485 data communications. It is recommended to use a shielded, low-capacitance twisted pair cable with an impedance of 120 ohm and a wire size (cross-sectional area) of 22 to 24 AWG (0.33 to 0.20 mm²). For more information, see Cable Selection .
The cable shield should be connected to earth ground at one location (preferred at the hosting controller) and should be connected through to the next segment at each device without additional connections to ground.
When the controller is installed in a space that handles conditioned air or return air, the Modbus network cables and IP network cables frequently must be plenum-rated to meet applicable building codes.
Whether you need to configure an RS-485 port to use for Modbus, or if there is a port configured for Modbus by default, varies depending on the RP-C controller model and its set (number) of ports. In this respect, the RP-C controller models are divided in the following three categories:
Models with two RS-485 ports (Com A and Com B):
(models with an “-F” in the product name)
RP-C Advanced: RP-C-12A-F-24V, RP-C-12B-F-24V, RP-C-12C-F-24V, and RP-C-16A-F-230V
RP-C Pro: RP-C-16B-F-24V and RP-C-16B-F-230V
Models with one RS-485 port (Com A):
EasyLogic RP-C (models with an “-M” in the product name): RP-C-12A-M-24V, RP-C-12B-M-24V, and RP-C-16A-M-24V
Models with three RS-485 ports (Com A, Com B, and Com C):
RP-C Pro Plus: RP-C-16C-F-230V
The Modbus communication parameters can be freely configured regardless of which RS-485 port on the RP-C controller that is used for the Modbus network. For more information, see RP-C Communication Ports .
You need to configure which RS-485 (RJ45) port on the RP-C controller to use for the Modbus network. You can configure to use either the RS-485 Com A or Com B port, which by default are configured for the sensor bus and room bus respectively. For more information, see Communication Ports on RP-C Models with “-F” in the Product Name .
You need to reconfigure the RS-485 (RJ45) Com A port on the RP-C controller to use for the Modbus network. The RS-485 Com A port is by default configured for the sensor bus. For more information, see Communication Ports on RP-C Models with “-M” in the Product Name .
You can directly use the RS-485 Com C port as it is configured by default for the Modbus network. For more information, see Communication Ports on RP-C-16C-F-230V .
Restrictions for Connecting Modbus Devices to the RP-C Modbus
The maximum number of Modbus devices that can be connected to the RP-C Modbus network, and the restrictions that apply to certain types of the devices and the maximum number of Modbus registers, vary depending on the RP-C controller model. In this respect, the RP-C controller models are divided in the following three categories:
RP-C Advanced: RP-C-12A-F-24V, RP-C-12B-F-24V, RP-C-12C-F-24V, and RP-C-16A-F-230V
EasyLogic RP-C (models with an “-M” in the product name): RP-C-12A-M-24V, RP-C-12B-M-24V, and RP-C-16A-M-24V
RP-C Pro and RP-C Pro Plus: RP-C-16B-F-24V, RP-C-16B-F-230V, and RP-C-16C-F-230V
The maximum number of Modbus devices that can be connected to an RP-C controller depends on the type of Modbus device and the number of Modbus registers.
The maximum number of Modbus registers that can be connected to and managed by an RP-C controller depends on the communication capacity of the controller's Modbus network.
The RP-C Advanced controller Modbus network supports up to 10 connected Modbus devices with the following restrictions:
Maximum of one KNX Modbus gateway (RP-C-EXT-KNX)
Maximum of 250 Modbus registers per network
64-bit Modbus registers are supported, which can be used in energy metering.
The KNX Modbus gateway has the default Modbus address 1. The address can be configured through the ETS. For more information, see Configuring the Modbus Device Settings in the KNX Modbus Gateway .
The maximum number of Modbus devices that can be connected to an RP-C controller depends on the type of Modbus device and the number of Modbus registers.
The maximum number of Modbus registers that can be connected to and managed by an RP-C controller depends on the communication capacity of the controller's Modbus network.
The EasyLogic RP controller Modbus network supports up to 10 connected Modbus devices with the following restrictions:
No KNX Modbus gateway (RP-C-EXT-KNX)
Maximum of 250 Modbus registers per network
64-bit Modbus registers are supported, which can be used in energy metering.
The maximum number of Modbus devices that can be connected to an RP-C controller depends on the type of Modbus device and the number of Modbus registers.
The maximum number of Modbus registers that can be connected to and managed by an RP-C controller depends on the communication capacity of the controller's Modbus network.
The RP-C Pro and RP-C Pro Plus controller Modbus network supports up to 20 connected Modbus devices with the following restrictions:
Maximum of one KNX Modbus gateway (RP-C-EXT-KNX)
Maximum of 1,000 Modbus registers per network
64-bit Modbus registers are supported, which can be used in energy metering.
The KNX Modbus gateway has the default Modbus address 1. The address can be configured through the ETS. For more information, see Configuring the Modbus Device Settings in the KNX Modbus Gateway .
Hardware Overview
RP-C Controllers
RP-C Models
Non-isolated RS-485 Adapter
RS-485 Power Adapter
Wiring
RS-485 Communications
Cable Routing
Cable Selection
RP-C Communication Ports
Communication Ports on RP-C Models with “-F” in the Product Name
Communication Ports on RP-C-16C-F-230V
Communication Ports on RP-C Models with “-M” in the Product Name
SpaceLogic RP-C Advanced
KNX Modbus Gateway RP-C-EXT-KNX
Spacelogic RP-C-EXT-KNX
Configuring the Modbus Device Settings in the KNX Modbus Gateway
ETS Database for the KNX Modbus Gateway