Methods for OMRON PLC to communicate remotely via MODEM - Dedicated Line Connection
OMRON PLCs provide the functionality to connect a modem to a PC. This is achieved by connecting the modem to both the PC and the PLC, and then running SSS or CPT software on the PC to remotely monitor and control the system and debug the program. The modem connection can be either a dial-up connection or a dedicated line connection. The following describes the method for implementing this functionality using a dedicated line connection.
Dedicated line connection
A dedicated line connection refers to a communication method where two modems communicate directly using a single 2-core or 4-core ordinary telephone line, without going through the PSTN public telephone exchange. This method is extremely useful when the distance between the host computer and the PLC is long, and the site lacks access to the PSTN telephone network. Generally, the distance from an ordinary telephone line to the telephone exchange is within 1 km, so a dedicated line connection should be sufficient within 1 km. The specific applicable distance needs to be tested by the user in practice.
The hardware requirements and wiring for dedicated line connections are basically the same as those for dial-up connections. The parameter settings for the modem, computer, and PLC are also the same as described above. The following only explains the differences between dedicated line connections and dial-up connections.
1. Modem Setup: Besides the requirement for dial-up connection, the most important aspect of a modem is that it must support leased lines. Some commercial modems currently on the market do not have leased line functionality; therefore, when selecting a modem, you should contact the manufacturer to confirm that it supports leased lines.
Configure the modem parameters as required above. Additionally, set the modem to leased line mode, designating one modem as the caller (Original) and the other as the receiver (Answer). Some modems supporting leased lines can be configured via buttons or other hardware methods on the front panel. If hardware configuration is not possible, you will need to configure and save the settings using AT commands through "HyperTerminal" as described in "Dial-up Connection". The corresponding AT command is: &L1: Set to 2-line leased line mode. After configuring the modem, connect it to the host computer and PLC respectively, and insert a telephone line with RG-11 plugs at both ends into the "LINE" port of the modem. Then power on all devices.
2. Using CPT and SSS: After the modem is powered on, the calling party (usually connected to a computer) will automatically initiate a call and establish a connection with the called party. A successful modem connection can be confirmed by observing the indicator (CD light) on the modem panel. After successful connection, run the SSS or CPT software on the computer and communicate with the PLC using the HOSTLINK method. In other words, a dedicated line connection simply replaces the serial communication cable between the computer and PLC in the HOSTLINK method with two automatically connecting modems.
