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If multiple analog input meters or transmitters are digitally addressed in command mode on an RS485 line using the Modbus RTU protocol or the Custom ASCII protocol, the rate becomes about 2 readings per second. Laureate meter and LT series transmitters support the Modbus RTU protocol and Laurel’s simpler ASCII character based Custom ASCII protocol. Both boards support the Modbus protocol and Laurel’s Custom ASCII protocol, as well as half-duplex or full-duplex RS485 communications. This robustness is the main reason why RS-485 is well suited for long-distance networking in noisy environment. Using a repeater, the main cable is divided into different segments, each of which can be up to 700 m in length and connect 32 devices (this number includes the repeaters). The main difference is, that pin 1 and 6 on the RJ11 socket of the MJ20-PRG module are used as power supply. At the receiver end the voltage difference should not be less than 0.2 Vdc. The difference between RS422 and RS485 is the fact that RS485 has the possibility to built a multi-point application. Laureate RS485 boards are available in versions with dual RJ11 jacks (ordering option 2, board P/N L485) and with dual RJ485 jacks (ordering option 4, board P/N LMOD).

These cables allow the dual RJ11 jacks of the RS485 option board of Laureate meters (digital interface ordering option 2) to be daisy chained and to be addressed digitally with no need for a hub. To connect an RS485 device or RS485 network to any PC or controller, the PC or the controller should provide RS485 interface also. The interface is normally terminated on a 4 wire screw block. Especially when the transmission is carried over a long wire outdoor, the wires is potential to carry the dangerous signal like lightning or other high voltage induction. RS485 is simpler because it uses only two wire (or a single pair) to carry out the data in bidirectional manner, using RS232, we need 3 wires at minimum to carry the data bidirectionally. If we want to connect a PC with an Unitronics PLC, for example for programming or debugging reasons, we need a connection cable which is on one side fitted with a female DB9 connector, and on the other side with an RJ11 jack.

The RS232-RS485 adapter circuit diagram is show below, RS232 DB9 is used as the RS232 port, while only a terminal block is used as RS485 connector. When in full RS232 mode, the six available pins are assigned to the most used RS232 signals. When in RS485 mode, only in 1 and 6 are reassigned. Should I use half-duplex or full-duplex RS485? RS-485, like RS-422, can be made full-duplex by using four wires. RJ11 jacks support half-duplex or full-duplex communications. With this boards, a CBL03 lines with RJ11 connectors can branch out to support an RS485 line consisting of three discrete wires. Both will work with RJ11 connectors and CBL03 cables. A challenge is that Laureate meters use RJ11 jacks, while Laureate LT series transmitters use screw-clamp connectors for three discrete wires. RS485 cable length can be as long as 1.2 km, while RS232 only about 25 meters. RS485 is specified for multi-point communicates where multiples devices have their own address on the same communication line, while RS232 is only specified for point-to-point communications. Ideally, the two ends of the cable will have a termination resistor connected across the two wires.

Our plans to upgrade our solar PV system this year are slowly progressing with installing a new Solis 1.5kW inverter and an EM112 Series Energy Meter, which have RS485 output and communicate using Modbus protocol. We then added the 10K pull-up and pull-down resistors to the RS485 Pi board and connected it directly to the Solis inverter. Then use front panel programming to set the baud rate, protocol, digital address, half or full duplex, and other available parameters. B then it is counted as a space (0 or on). The wide supply voltage range also means that you can allow for a significant voltage drop along the bus (e.g., when using a bus cable of considerable length). As a rule of thumb, the speed in bit/s multiplied by the length in metres should not exceed 108. Thus a 50-meter cable should not signal faster than 2 Mbit/s. This cable provides a USB type A connector for the PC end and an RJ11 connector for the meter end. What cable should I use to connect meters with an RS485 port to the USB port of a PC? With RS485 it is possible to set-up a multi-point application with one master and several slaves.