Tunnel – Using API to send SMS to external PLC devices connected to COM1 at the same time that the 4G-RS232 tunnel is active

Scenario details:

• From the central offices we need to access periodically via 4G the PLC serial port to send instructions and collect results. To access it we’ll use MTX-Tunnel as a 4G-RS232 gateway
• MTX-Tunnel must always have the IP session established to be able to access the PLC device at any moment. It will use the port TCP 20010
• The PLC device should be able to send an SMS alarm at any moment. PLC is connected to MTX-Tunnel via the only serial port, so the serial 4G tunnel can coexist with seding AT commands by the PLC using the same serial port (to send the SMS)

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

Config.txt configuration file:

Configuration

Observations

COMM_baudrate: 115200 COMM_bitsperchar: 8 COMM_autocts: off COMM_autorts: off COMM_stopbits: 1 COMM_parity: none GPRS_apn: movistar.es GPRS_login: MOVISTAR GPRS_password: MOVISTAR GPRS_timeout: 0 MTX_model: MTX-4G-JAVA-T MTX_mode: server MTX_ATMux: on MTX_ping: 30 MTX_pingIP: 8.8.8.8 TCP_port: 20010 FIREWALL_enabled: off TELNET_enabled: on TELNET_login: user TELNET_password: 1234 TELNET_port: 20023

Serial port baudrate 8 bit data CTS hardware control disabled RTS hardware control disabled 1 bit stop No parity GPRS APN from your network operator GPRS Login GPRS Password Modem is permanently connected to GPRS MTX terminal modem model used TCP server mode AT multiplexing mode on serial port enabled Minutes for connectivity supervision ping Connectivity supervision IP address TCP port for 4G-RS232 Firewall disabled Modem’s Telnet unabled Telnet username Telnet password Telnet port

Detailed explanation:

The simplest way to solve this scenario is to use an AT command multiplexer. This allows you to send AT commands at same time that the GPRS-serial tunnel is established. Enable the MTX_ATMux parameter to “on” to activate the multiplexer.

The AT commands must have a special format, between tags:

<MTXTUNNEL></MTXTUNNEL>

In the example, to send “WARNING HIGH TEMPERATURE REACHED” to the end phone number 666123456 the command will be:

<MTXTUNNEL>AT^MTXTUNNEL=SMS,666123456,WARNING HIGH TEMPERATURE REACHED</MTXTUNNEL>

The command is interpreted and MTX TUNNEL executes it. The AT response will also be between the same tags.