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If handshaking is not necessary, an ordinary 4 wire telephone cable could be used, provided that the pins are cross-connected as shown in the picture below. The layout for this cable is shown below. The POE version makes this a single cable connection that will allow monitoring from anywhere in the world; anywhere with internet access that is. Additionally, the Brainchild's standard Ethernet and optional RS-232/RS-422/RS485 communication enable users to access data onsite from a remote location via the RS serial interface or Ethernet networking. The Jazz PLC series from Unitronics are not standard equipped with a RJ11 connector for serial communications. 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. The two jacks are for RS485 cable in and RS485 cable out. For RS232 a crossover cable is used where pin 1 is connected with pin 6 at the other connector, pin 2 with pin 5, etc. This interconnects the transmit and receive signals of both PLCs, and also the handshaking signals DTR and DSR. Pin 1 and 6 however are reassigned to the A and B lines when the port is used in RS485 mode.

Two Tibbo Project System (TPS), Gen. 2-compatible Tibbo BASIC applications for the setup and testing of Bus Probes are available: BP-Tester-UI and BP-Tester-Web. Bus Probes are a family of low-power environmental sensors with an RS485 interface. The twin consists of two conductors that are twisted together. A symmetrical pin-layout allows two DTEs, data terminal equipment, to be connected directly without use of a modem or other DCE, data communication equipment. The symmetrical pin layout of the RJ11 sockets on the Unitronics PLCs allows an easy way of interconnecting the PLCs with both RS232 and RS485 communications. This MJ20-PRG module clicks in the PLC and provides one RJ11 socket for serial communications with a PC. The main difference is, that pin 1 and 6 on the RJ11 socket of the MJ20-PRG module are used as power supply. 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). The two jacks are wired in parallel by circuit traces on the circuit board.

Each device has a communication port with two terminals, which are indicated for the sake of convenience as A and B. In these two terminals the communication cable is connected so that all the devices that take part in the communication are connected in parallel. If on the other hand each terminal can accept only a single cable, a proper branch must be created using three auxiliary terminals for each instrument to be connected. The 735 series are desk top terminals and the companion 720 wall mount units. In RS232 mode all pins are used for RS232 signals. This module is powered by the RS232 port from the connecting computer. The only way to add RS232 capabilities to the Jazz PLCs is by using the MJ20-PRG programming port add-on module. 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. This cable provides a USB type A connector for the PC end and an RJ11 connector for the meter end.

The end resistance must be used only at the ends of the main cable. Class I must say i, Category A man or woman regarded detrimental sites. Otherwise a full 6 wire cable must be used. Therefore for RS485 communications no crossover cable is used. Note that these cables are different from4-wire telephone cables or crossover cables. What RJ11 cables should I use with RS485? The diagram below shows a basic RS485 cable for use with the RJ11 socket on Unitronics PLCs. The RJ11 socket in the Unitronics PLCs provides six signal pins. The normal way to implement this is with a two wire system with differential signal levels. Two wire telephone cables will not function because in that case the ground signal levels on both sides will be floating. Use Laurel’s 6-wire data cables CBL03-1 (1 ft) and CBL03-7 (7 ft) to interconnect meters if these lengths fit your application. Both boards support the Modbus protocol and Laurel’s Custom ASCII protocol, as well as half-duplex or full-duplex RS485 communications. If the PC is connected to the multiple Laureate instruments on an RS485 bus via an Ethernet-to-RS-485 gateway board or a USB-to-RS485 gateway board, use Laurel’s free XLOG2 datalogging software.