RS485 RJ45 Interface Board P/N LMOD for Laurel Electronics 1/8 DIN Instruments

The Laureate P/N LMOD interface board with dual RJ45 jacks allows multiple Laureate meters, counters, timers and remote displays to be connected to the same RS485 line.

The LMOD board is not recommended for new designs, but it remains readily available from Laurel for existing designs. For new designs, use the functionally equivalent L485 board with dual RJ11 jacks. That board is better supported by Laurel interface cables and is designed for easy interface to Laurels gateway boards, which are LUSB485, LNET485, LNET1485, LWIFI485, LWFIX485. The gateways boards all provide an RJ11 jack for connection to an RS585 bus with up to 31 Laureate instruments.

The dual jacks of the LMOD board are wired in parallel as for the recommended L485 board. This allows multiple instruments to be daisy-chaned using data cables (or patch cords) with RJ45 plugs; however, such data cables are not available from Laurel. Laurel's alternative L485 board with dual RJ11 jacks is supported by our RS485-to-USB converter cable (P/N CBL06) for data I/O and for programming by a PC running our Instrument Setup (IS) software. It is also supported by our 6-wire data cables (or patch cords) with RJ11 plugs (P/N CBL03) to daisy-chain meters without use of a hub.

The LMOD or L485 boards can be configured for full-duplex or half-duplex operation using jumpers. Transmission distances up to one mile are possible.To avoid signal reflection with long signal lines, a 120-ohm termination resistor can be slected via jumpers. The meter, counter or timer should be programmed for full duplex operation, even if the RS485 board is jumpered for half duplex.

Two serial protocols are user-selectable for RS485: Modbus RTU and Custom ASCII. For detailed information on our protocols, please see our communication user manuals.

• The Modbus RTU protocol is an international standard and allows Laureates to share the same RS485 data lines with non-Laurel devices. It supports up to 247 digital addresses. Use of more than 31 Laurel RS485 Modbus boards requires repeaters for impedance reasons. Modbus RTU works in a master-slave (or query-response) mode, and its use requires an external Modbus master, which is typically a PC. Meters with a thermocouple input and using the Modbus RTU protocol should be set to full duplex.
• Laurel's Custom ASCII protocol is the simpler of the two protocols and uses ASCII strings. It is recommended if the only devices on the RS485 data line are Laureate meters. It supports up to 31 digital addresses. It can be set to a command mode under control of an external master, or to a continuous streaming mode where data is output at specified intervals at rates up to 60 per second.

The signal levels of tLaureate RS485 boards are compliant with the EIA/TIA-485 standard. Devices by different manufacturers can share the same RS485 data line, provided that their connectors are wired appropriately.