In order to avoid errors when many devices are connected, cables of the same colour should be used for all the connections to the terminals A and cables of the same colour should be used for all the connections to the terminals B of the various devices (e.g. white for A and blue for B). This makes it easier to identify cabling errors. Henceforth, we shall consider Slave devices to be measuring instruments with serial communication, even if the cabling is similar for all Modbus devices. The cabling of the industrial communication systems (Modbus RS485) is different in some ways from the cabling used for power cabling and the electrician may experience some difficulties if he is not an expert in Modbus communication networks. RS-485 does not define a communication protocol; merely an electrical interface. 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. The two values provide a sufficient margin for a reliable data transmission even under severe signal degradation across the cable and connectors.

I recently bought some RS485 cable, it had two pairs, both had stripes. Enabling RS485 on the Serial2 port is parallel to the process described above. The advantage of using Serial1 for RS485 is that the Serial1 RS485 signals are also available on the Docking Panel, while the Serial2 RS485 signals are available only on the PDQ Board’s Serial Communications Header. Typing a carriage return at the terminal should now produce the familiar "ok" response via the Serial2 port. For an off, mark or logic 1 state, the driver's A terminal is negative relative to the B terminal. For an on, space or logic 0 state, the driver's A terminal is positive relative to the B terminal. Because a mark (logic 1) condition is traditionally represented (e.g. in RS-232) with a negative voltage and space (logic 0) represented with a positive one, A may be considered the non-inverting signal and B as inverting. The issue also exists in programmable logic controller applications. Although many applications use RS-485 signal levels, the speed, format, and protocol of the data transmission are not specified by RS-485. Communications capability is essential for many instrument control applications. Depends what you mean by a serial cable - Fibre, Ethernet, RS232, RS485, RS422, USB, HDMI, SMPTE292 are all examples of serial communications media.

The primary serial port, Serial1, is supported by the 68HC11's on-chip hardware UART (sometimes called a USART), and does not require interrupts to work properly. Owing to hardware constraints, if modem handshaking is needed on UART channel 1, then channel 1 must be configured for RS232, and channel 2 cannot be configured for RS232 communications. In general if you are not connected to a modem the handshaking lines can present a lot of problems if not disabled in software or accounted for in the hardware (loop-back or pulled-up). Now there was certain instances I used STP wire for rs485 because I had a lot of devices connected in a long run chain (DMX512 lighting fixtures). It seems if there is a lot of RFI in the installation, shielded twisted cable can be justified. With Modbus, BACnet and Profibus, A/B labeling refers A as the negative green wire and B as the positive red wire, in the definition of the D-sub connector and M12 circular connector, as can be seen in Profibus guides.

3106A is what I typically use to wire balanced audio. These manufacturers all agree on the meaning of the standard, and their practice is in widespread use. Interoperability of even similar devices from different manufacturers is not assured by compliance with the signal levels alone. Is the striping set by manufacturers or have any meaning beyond indicating a pair? In fact, the program works the same as it did before, but now it is using the secondary serial port instead of the primary port - and you didn’t even have to recompile the code! Large phone cables have solid with white stripes, and solid. I'm mostly used to ethernet with a pair consisting of completely solid and white with a stripe. Note that the local and the remote must share a common ground, so a minimum of 3 wires are required for half duplex RS485 communications: a pair of transceive wires and a common ground.