COM-ME1 ModBUS TCP interface application note

COM-ME1 ModBUS TCP interface

You can easily connect the RKC Instrument FZ, GZ and multizone SRZ system to your HMI/SCADA/PLC system via ModBUS TCP protocol over any existing ethernet connection, also in parallel to other connections in your factory network.

For this RKC Instrument developed the COM-ME1 interface convertor.

Supported models:

  • FZ110
  • FZ400
  • FZ900
  • GZ400
  • GZ900
  • SRZ-TIO-A 4 channel process/temperature controller
  • SRZ-TIO-B 2 channel process/temperature controller
  • SRZ-DIO 8x digital input 8x digital output
  • SRZ-CT 12x current measurement for heating element monitoring

Leaflet COM-ME-1 ModBUS TCP FZ & GZ series and SRZ system
Instruction manual COM-ME-1 ModBUS TCP FZ and GZ series
Instruction manual COM-ME-1 ModBUS TCP SRZ system

Communication convertors for other fieldbuses

Example application note: connect a RKC Instrument SRZ multichannel system to a Pro-face GP4301TAD HMI/SCADA/PLC touchpanel

Connecting a RKC SRZ system to a Pro-face GP4301TAD touchpanel can easily be done using the COM-ME1 interface. 

General remark regarding ModBUS RTU/TCP:

  • ModBUS RTU: serial 2 or 3 wire RS-485 connection
  • ModBUS TCP: ethernet connection using RJ-45 ethernet connectors and standard ethernet cabling

This procedure can also be used for any other PLC/PC/ HMI/SCADA system with an ethernet port supporting the ModBUS TCP protocol.

Items you need:

  • RKC COM-ME1 interface module (connected to):
  • SRZ system containing at least 1 SRZ module (TIO, DIO or CT)
  • Pro-face GP4301TAD touchpanel (other Pro-face types or any other modern touchpanel with ethernet interface with ModBUS TCP protocol support)
  • Ethernet cable (1:1 since the Pro-face screen has an auto-sensing ethernet port)
  • 24Vdc power supply
test setup for testing COM-ME1 to Pro-face communication

Test setup: from left to right:

  • 24Vdc power supply
  • RKC COM-ME1 with SRZ-TIOAC (4 channel)
  • Pro-face GP4301TAD touchpanel

1. Configure the settings on the TIO and DIO modules for communication with the COM-ME1 with ModBUS RTU RS-485 38400bps 8N1

In this example the communication between the COM-ME1 and the SRZ TIO/DIO module(s) will be performed using a serial ModBUS RTU protocol over a 3-wire RS-485 communication interface. This interface wilL run over the SRZ system backplane where the module(s) are clicked on. You don’t need to wire this yourself.

The communication speed will be 38400 bps (bits per second) with 8 databits, no parity and 1 stopbit (8N1).

Setting the ModBUS RTU addresses of the TIO/DIO modules
TIO module rotary switch settings for modbus RTU address
ModBUS RTU address setting of TIO/DIO modules

Note: the TIO/DIO module(s) only accept the new address settings after a power cycle!

The rotary switch on the front of the TIO/DIO module(s) are the ModBUS RTU serial protocol address settings.

The COM-ME1 communicates with these TIO/DIO modules via a ModBUS RTU RS-485 serial connection over the backplane of the modules. After reading/writing all parameters from/to them it will map these parameters inside its ModBUS TCP list for further communication over that interface.

Set the rotary switch of the 1st TIO module to 0 (meaning ModBUS RTU address 1), the 2nd to setting 1 (meaning ModBUS address 2) etc.

Set the rotary switch of the 1st DIO module also to 0 (meaning ModBUS RTU address 17, since the DIO’s start automatically and always at ModBUS RTU address 17). The rotary switch of the 2nd DIO to 1 (meaning address 18) etc.

Note: The TIO’s can have ModBUS RTU address 1-16 (rotary switch 0-F) and the DIO modules 17-33 (rotary switch 0-F).

Setting the TIO/DIO module communication interface to ModBUS RTU 38400bps N81

The TIO/DIO modules are clicked on a backplane printed circuit board (PCB). You can push the latch on the underside of each module in and rotate them upwards to remove them from the backplane. Only do this with the power switched off, to prevent damage to the module(s).

On the side of each TIO/DIO/CT module you will find a very small 8 position dipswitch. This switch sets the type of communication protocol (RKC ASCII or ModBUS RTU), the communication speed and the amount of databits, stopbits and the type of parity.

Set each module (except the COM-ME1!!!) to ModBUS RTU interface, 38400bps, N81 (no parity, 8 databits, 1 stopbit).

Note: Use a proper small screwdriver to make these settings, otherwise the small switches get damaged.

TIO dipswitch setting 38400bps 8N1 Modbus RTU
detailed DIPswitch settings for all the SRZ modules (except the COM-ME1!!!)
RKC SRZ dipswitch setting 38400bps N81

DIPswitch settings for all the SRZ modules (except the COM-ME1!!!) set to ModBUS 38400BPS N81. From left to right: 2x up, 2x down, 2x up, 2x down

SRZ TIO and DIO dipswitch setting for Modbus 38400BPS 8N1

Note: the TIO/DIO module(s) only accept the new address settings after a power cycle!

2. COM-ME1 dipswitch and rotary switch settings

Set the rotary switches on the COM-ME1 all to 0 and the small DIP-switches on the side of the module as follows. Use a proper small screwdriver to make these settings, otherwise the small switches get damaged.

DIPswitch settings on the side of the COM-ME1: From left to right: 1x down (switch 1), 2x up (switch 2 & 3), 5x down (switch 4 to 8)

rotary switch settings of the COM-ME1 (all 0)

3. Configure COM-ME1 interface module fixed IP address 10.0.0.112 port 502

First we will set the IP address of the COM-ME1 module, that is, the IP address where it can be reached by the Pro-face touchpanel. We will set it to 10.0.0.112.

We will make use of the handy and easy to use COM-KG configuration interface (see below) in combination with the free downloadable PROTEM2 software from RKC Instrument on your windows PC.

You can also configure it using the dipswitches on the side and the rotary switches on the front. But that is not so easy as with the COM-KG interface. 

*) for instructions on how to use the COM-KG interface with the RKC PROTEM2 configuration tool, see below.

We will make use of the standard port number that is almost always used for ModBUS TCP: port number 502

COM-ME1 IP address configuration for Modbus TCP
set ENG(1) settings in COM-ME1 to the correct ModBUS TCP slave address of the COM-ME1
  • Make sure the PROTEM2 software has active communication with the COM-ME1 module by switching it to online in ENGINEER mode (parameter change allowed)
  • select the COM-ME1 ENG(1) settings
  • set the IP address to 10.0.0.112
  • set the TCP port number to 502.

4. Configure COM-ME1 interface module to ModBUS RTU 38400bps N81

COM-ME1 communication parameters Modbus RTU 38400bps N81
set ENG(2) settings in COM-ME1 to ModBUS RTU communication protocol to 38400bps N81
  • Make sure the PROTEM2 software has active communication with the COM-ME1 module by switching it to online in ENGINEER mode (parameter change allowed)
  • select the COM-ME1 ENG(2) settings
  • set the Host communication protocol to 1 (ModBUS)
  • set the Host communication communication speed to 3 (38400bps)
  • set the host communication data bit configuration to 0 (8 databits, no parity, 1 stop-bit)
  • leave the host communication interval time on 10ms
  • leave the host communication device address on 0 

Note: the COM-ME1 module only accepts the new address settings after a power cycle!

Note: on the ENG(2) page you can also see the number of TIO/DIO/CT modules that were detected by the COM-ME1. If this is not correct there is something wrong with the connections or communication settings.

5. Configuration of the IP address of a Pro-face GP4301TAD touchpanel

In order to set the IP address of a Pro-face touchpanel, we first have to set it in so-called “offline mode”. This is done as follows:

Setting the touchpanel to offline mode is (at first) not easy.

  • push intermittently and fast between the corners 1 and 2 on the screen, but inside the black square around the screen
  • use 2 index fingers, with only 1 finger is not fast enough
  • You need to push the screen intermittently (first push 1 and quickly after that 2), so don’t push both fingers at the same time.
  • If you see a gray bar appear: STOP immediately, don’t push anywhere anymore!
Setting Pro-face touchpanel to offline mode
push corners quickly intermittently, but not at the same time
go to offline mode for touchpanel setup
  • Push Offline (sometimes you need to enter the level 15 password, see the application manual appendix A for passwords)
  • Sometimes you need to enter a system password, this is 15 + the ENT key (enter)
  • select Main Unit
  • select Ethernet
  • set Port to 8000
  • set Primary DNS to 10.0.0.111 (the IP address of the Pro-face touchpanel)
  • set Secondary DNS to 0.0.0.0
  • Push LAN
set IP address
  • set IP Address to 10.0.0.111
  • set Subnet Mask to 255.255.255.0 (Note: this corresponds to the COM-ME1 ENG(2) subnet mask CDIR setting of 24 which is equal to 255.255.255.0)
  • set Gateway to 10.0.0.254
set IP address
  • push Exit
  • Confirm by pushing on Yes
save settings and terminate offline mode

The Pro-face touchpanel will now reboot with the correct settings for the IP address (set to 10.0.0.111) so it can communicate with the COM-ME1 unit.

Note: The Pro-face ethernet interface port is auto sensing, so you can use a 1:1 straight ethernet cable between the COM-ME1 1st ethernet port and the Pro-face touchpanel.

Note: the 2 ethernet ports on the COM-ME1 are wired in parallel for a ethernet daisy chain, so it does not matter which ethernet port you connect on the COM-ME1.

6. Configuration of the ModBUS TCP interface in the Pro-face GP-Pro Ex application

Make a new project in GP-Pro Ex for a GP-4301TAD touchpanel and configure the interface as follows:

*) note: the Pro-face touchpanel is the ModBUS TCP master (takes initiative to communicate) and the COM-ME1 is a ModBUS TCP slave (reacts to commands from the master).

Configuring the communication interface in GP-ProEx for ModBUS TCP master
setting IP address of the COM-ME1 ModBUS TCP slave in the GP-Pro Ex application

Here are the Device/PLC settings for the ModBUS TCP master interface:

  • select manufacturer “Schneider Electric SA” (don’t select another one!!!)
  • select MODBUS TCP Master
  • select Port Ethernet(TCP)

After selecting this interface, push Add Device and configure PLC1 (or another name you choose) as follows:

  • IP Address 10.0.0.122 (note: this is the IP address that we set in the COM-ME1)
  • Port No: 502 (default for Modbus TCP)
  • Unit ID: 1
Reading the 1st temperature measurement channel of the 1st TIO module (rotary switch setting 0: ModBUS RTU address 1)
  • Now we have to check on which ModBUS TCP address inside the COM-ME1 module the ModBUS RTU address of the 1st channel of the 1st TIO module is mapped by the COM-ME1.
  • See the  – Instruction manual COM-ME-1 ModBUS TCP SRZ system (above on this page)
  • Check the communication data list for the Z-TIO module
ModBUS TCP address in COM-ME1 of ModBUS RTU address 0 of 1st channel in 1st TIO
  • The Measured Value (PV=process value) is mapped inside the COM-ME1 ModBUS TCP data list as decimal address 508 (decimal) up to 571 (decimal). Up to 16x 4 channel TIO modules can be connected, the 4th channel of the 16th TIO module is 508+(15 modules*4 channels)+3 (4th channel)=571 (decimal)
  • This list contains all measured values for all TIO modules that are connected to the COM-ME1. So max. 4×16=64 measurements are mapped.
  • The 1st TIO has 4 (or 2) channels. So the 1st measurement on the 1st TIO of the COM-ME1 module corresponds to decimal address 508.
  • Now, with ModBUS interfaces in GP-Pro Ex in general you must always add 1 to this number, to get the correct address: so 508+1=ModBUS TCP address 509 (decimal) (and the last address 4th channel 16th TIO is 571+1=572)
  • Since this is a read/write 16 bit register, the actual ModBUS TCP address inside the COM-ME1 is 400509 decimal. It is in the 4xxxxx range, since the SRZ registers are read/write 16-bit word registers. Note that not all registers can be written (i.e.  PV temperature measurement), please check the communication data attribute for this (RO=read only RW=read/write)
ModBUS TCP address in COM-ME1 of ModBUS RTU address 0 of 1st channel in 1st TIO

Since the TIO channel is configured for measurement with 1 decimal behind the comma, you set the display settings to 1 decimal place in order to show that extra decimal properly on the touchpanel.

1 decimal place setting

After connecting the touchpanel to the COM-ME1 first ethernet port, and loading the GP-Pro Ex application into the touchpanel, the temperature measurement of the 1st channel of the 1st TIO is displayed properly on the touchpanel.

process value of 1st channel of 1st TIO module

With correctly running communication between the TIO/DIO modules and the touchpanel, you see these green lights and the HRTBT (heartbeat) led slowly flashing green.

led status with correct operation

If there is something wrong in the cabling, the settings in either the COM-ME1 , the GP4301TAD touchpanel or the Pro-face project settings, you get a TCP connection error. 

Please review the settings above to check if you made a mistake somewhere. Don’t forget the cabling.

communication error due to misconfiguration

Please note, that proper communication is only possible with 24Vdc connected to the COM-ME1/TIO/DIO modules. You only need to connect on 1 position the 24Vdc, for the rest of the modules the power is running over the backplane of the SRZ system.

7. Monitoring the communication with the COM-ME1

Monitoring the communication after establishing the connecting is very important. Here is some advice on how to do this in combination with the COM-ME1 module.

Monitoring communication between the HOST (PLC/HMI/SCADA/PC) and the COM-ME1

If the ethernet connection is not online, your PLC/HMI/SCADA/PC IO port driver should give you an alarm signal when you try to read a ModBUS TCP register from the COM-ME1. Please monitor this in your application.

In Pro-face GP-Pro Ex: monitor bit [PLC1]#H_ErrorStatus for this

  • 0 (false): communication ok
  • 1 (true); communication not ok
monitor bit [PLC1]#H_ErrorStatus for communication errors

Please check the documentation of your specific host system for checking communication errors with your specific interface and driver.

Monitoring communication between the COM-ME1 and the connected SRZ TIO/DIO module(s)

If the communication between the COM-ME1 and the SRZ system is not online, you will get all 0 (zero) values in the COM-ME1 ModBUS TCP registers that are used for mapping TIO/DIO modules. This is an indication the ModBUS RTU host communication from the COM-ME1 to the SRZ system is not online.

You can also monitor the address showing the total number of connected modules that the COM-ME1 is detecting.

Monitor the address showing the total number of connected modules that the COM-ME1 is detecting. In the COM-ME1 this is ModBUS TCP address 400307.

  • 0 (zero): no modules detected by the COM-ME1
  • keep monitoring the value other than 0: if 1 (or more) SRZ modules fail to communicate, this number goes to a lower value
monitor number of connected SRZ modules connected to the COM-ME1
Detection of communication error between COM-ME1 and SRZ TIO module(s)

For detection of proper communication between the COM-ME1 and each separate SRZ-TIO module, we suggest using the read only parameter Z-TIO Interval time that is in the ENG(6) parameters of each TIO.

The ModBUS TCP register mapped inside the COM-ME1 for the 1st connected TIO is 37AC hexadecimal, 14252 decimal + 1 = [PLC1]414253 in GP-Pro EX. 

Use Z-TIO interval time for monitoring communication between COM-ME1 and TIO
Monitor COM-ME1 address 414253 for 1st TIO

Monitor the ModBUS TCP address 414253 for the 1st TIO with your PLC/HMI/SCADA/PC system. If this value becomes 0, there is no communication between the COM-ME1 and the 1st TIO module.

Do the same with the other TIO modules (other addresses).

Detection of communication error between COM-ME1 and SRZ DIO module(s)

For detection of proper communication between the COM-ME1 and a SRZ-DIO module, we suggest using the read only parameter Z-DIO Interval time that is in the ENG parameters of each DIO.

The ModBUS TCP register mapped inside the COM-ME1 for the 1st connected DIO is 469C hexadecimal, 18076 decimal + 1 = [PLC1]418077 in GP-Pro EX. 

Use Z-DIO interval time for monitoring communication between COM-ME1 and DIO
Monitor COM-ME1 address 418077 for 1st DIO

Monitor the ModBUS TCP address 418077 for the 1st DIO with your PLC/HMI/SCADA/PC system. If this value becomes 0, there is no communication between the COM-ME1 and the 1st DIO module.

Do the same with the other DIO modules (other addresses).

Note: for a SRZ CT current measurement module, monitor the Z-CT ENG CT Interval time. For the 1st CT module this is 659C hexadecimal, 26012 decimal + 1 = [PLC1]426012 in GP-Pro EX.

Short video that shows the COM-ME1 ModBUS TCP addresses during communication errors

This short movie shows communication error information in the ModBUS TCP registers of the COM-ME1 module.

  • Communication error between Pro-face GP4301TAD HMI touchpanel and the COM-ME1 module: ethernet cable between COM-ME1 and Pro-face GP4301TAD disconnected/connected: comms error status bit
  • Communication error between COM-ME1 and 1st TIO module: 1st TIO module removed from the backplane and installed again (also check number of connected modules)
  • Communication error between COM-ME1 and 1st DIO module: 1st DIO module removed from the backplane and installed again (also check number of connected modules)

COM-KG configuration/communication interface

With the COM_KG you can configure the COM-ME1 easily via a USB port to your laptop / desktop.

Can also be used as a generic USB to RS-485/422 interface

Don’t forget to specify the correct RKC equipment interface cable when ordering, see more information for details.

Leaflet COM_KG
Instruction manual COM_KG