Tunnel – Providing IP to Master Modbus RTU and Modbus RTU slaves

Scenario details:

• We have a PLC with Modbus RTU RS485 communications which, acting as master, performs periodic readings of 3 slave devices also with Modbus RTU RS485 communications
• It is necessary to replicate that same scenario, with the same RS485 devices, but with IP communications, since it is not possible to carry out a wiring when the different elements are located at kilometers distances between them
• SIM cards will be used with private APN, so each device will have a MTX-Tunnel modem with fixed IP address to facilitate communications and increase security

Solution: MTX-Tunnel firmware + MTX-Java-IoT/MTX-Java-T/MTX-Java-T2

Configuration example (config.txt file) for the indicated scenario. MTX-Tunnel MASTER:

Configuration

Observations

COMM_baudrate: 9600 COMM_bitsperchar: 8 COMM_autorts: off COMM_autocts: off COMM_stopbits: 1 COMM_parity: none GPRS_apn: movistar.es GPRS_login: MOVISTAR GPRS_password: MOVISTAR GPRS_timeout: 0 MTX_PIN: 0000 MTX_mode: udp MTX_model: 199801393 MTX_ping: 35 MTX_pingIP: 8.8.8.8 SMS_allPhones: on SMS_sendIP: on SMS_ATEnabled: on SMS_ATResponse: on FIREWALL_enabled: off TELNET_enabled: on TELNET_login: user TELNET_password: 1234 TELNET_port: 20023 UDP_IP: 10.1.1.10@1,10.1.1.20@2,10.1.1.30@3 UDP_ localPort: 20010 UDP_ remotePort: 20010

Serial port baud rate Number of bits No flow control No flow control 1 stop bit No parity APN GPRS provided by the GSM operator GPRS Login GPRS Password Modem is always GPRS connected SIM Card PIN UDP communications will be used MTX modem model Ping every 35 minutes without comms IP address to ping Send SMS with commands from any phone Modem responds with IP to missed call or SMS It is possible to send commands to MTX via SMS MTX responds with SMS to a sent SMS command It’s possible to connect to the modem from any IP We enable the Telnet of the modem Login for Telnet Password for Telnet Telnet port for remote configuration changes IPs and slave Modbus RTU address are indicated Local communications UDP port Remote communications UDP port

Configuration example (config.txt file) for the indicated scenario. MTX-Tunnel SLAVES:

Configuration

Observations

COMM_baudrate: 9600 COMM_bitsperchar: 8 COMM_autorts: off COMM_autocts: off COMM_stopbits: 1 COMM_parity: none GPRS_apn: miapn.movistar.es GPRS_login: MOVISTAR GPRS_password: MOVISTAR GPRS_timeout: 0 MTX_PIN: 0000 MTX_mode: udp MTX_model: 199801393 MTX_ping: 35 MTX_pingIP: 8.8.8.8 SMS_allPhones: on SMS_sendIP: on SMS_ATEnabled: on SMS_ATResponse: on FIREWALL_enabled: off TELNET_enabled: on TELNET_login: user TELNET_password: 1234 TELNET_port: 20023 UDP_IP: 10.1.1.1 UDP_ localPort: 20010 UDP_ remotePort: 20010

Serial port baud rate Number of bits No flow control No flow control 1 stop bit No parity APN GPRS provided by the GSM operator GPRS Login GPRS Password Modem is always GPRS connected SIM Card PIN UDP communications will be used MTX modem model Ping every 35 minutes without comms IP address to ping Send SMS with commands from any phone Modem responds with IP to missed call or SMS It is possible to send commands to MTX via SMS MTX responds with SMS to a sent SMS command It’s possible to connect to the modem from any IP We enable the Telnet of the modem Login for Telnet Password for Telnet Telnet Port for Remote Configuration Changes Modbus master IPs are indicated Local communications UDP port Remote communications UDP port

Details:

• To solve this scenario UDP communications are used. Each time the modem is connected to the master PLC it receives a communication frame. Modbus analyzes the received frame by looking for the Modbus RTU address of the slave to which it is addressed. Once the address is found, the frame is sent only to the IP associated with the corresponding slave modbus RTU device
  • Example for the following configuration:
  • UDP_IP: 10.1.1.10@1.10.1.1.20@2.10.1.1.30@3
• If the master modem receives a modbus RTU frame and verifies that the destination address is for the slave device with address modbus @2, it forwards the received frame to the associated address, in this case 10.1.1.20.
• Other devices on the market forward the frame to all associated devices, with the consequent problem of increasing data traffic and, therefore, higher economic cost and lower communication speed
• Do not forget to establish a communication timeout in the master PLC of at least 2 seconds