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Having a second serial port is also handy for system debugging. In summary, the code provided for implementing the second serial port is very flexible and can be used to support dual concurrent communications ports. For this reason, frame-level cyclic redundancy checks are much more widely used for validating data from serial links, network connections and storage media. The connection between two or more elements (drivers and receivers) should be considered a transmission line if the rise and/or fall time is less than half the time for the signal to travel from the transmitter to the receiver. Since it uses a differential line over twisted pair (like EIA-422), it can span relatively large distances (up to 4000 feet or just over 1200 metres). This method is one of the simple and easy to implement methods to transfer the data over long distances. This 6 ft long cable comes with a USB connector on one end and the red and yellow tipped plugs and does not require a driver if used with Windows 7 or later versions. The specification allows for data transmission from one transmitter to one receiver at relatively slow data rates (up to 20K bits/second) and short distances (up to 50Ft. @ the maximum data rate).

Standards have been developed to insure compatibility between units provided by different manufacturers, and to allow for reasonable success in transferring data over specified distances and/or data rates. The main reason behind using these Ethernet Cables over normal wires is that they provide much better protection against noise creeping in and distortion of the signal over high distances. Nowadays, we mostly use Wi-Fi for internet connectivity but earlier we used to use Ethernet cables going to each personal computer to connect it to the internet. When we think of long-distance data transfer, we instantly think about connecting to the internet via Ethernet cables. 2 Alphanumeric LCD, and MAX485 UART to RS485 converter IC connected to each end of an Ethernet Cat-6E cable via an RJ45 connector. DTECH USB RS485 adapter cable devices with FTDI chipset allows you to connect RS422 or RS485 serial devices to your computer via USB. The QScreen Controller combines an embedded computer based on the 68HC11 microcontroller with a touch panel and LCD (liquid crystal display) graphic user interface (GUI) that is ideal for instrument control and automation. Now in the loop, we check if there is anything available on the serial port and then read the data and since the incoming data is an integer, we parse it and display on the connected LCD.

Application fields: Factory automation system, Distributed control system, Other 485/422 serial device wireless network, LED INFO display equipments, PLC control and management, SCADA, measuring instruments and monitoring system, CNC management, Medical treatment/medication automation, Building automation, Check on work attendance/ Human resource management. A break sequence forces the serial output to a logic low (space) at the UART. By setting this output LOW, the slave’s input /SS is pulled LOW. Here again, we start with including the standard library for driving the LCD and declare the D8 pin of the Arduino Nano as an output pin which we will later use to declare the MAX485 Module as a transmitter or Receiver. Similarly, when establishing the transmit mode, the application software is responsible for ensuring that the RS485 receiver is not disabled until all expected characters have been received. 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). 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.

The Electronics Industry Association (EIA) has produced standards for RS485, RS422, RS232, and RS423 that deal with data communications. Like RS232, the data bits are transmitted in reverse order, with the least significant bit transmitted first. The secondary serial port is connected similarly except that the onboard connection of RTS to CTS, and DSR to DTR are permanent. The RS232 protocol provides for four handshaking signals called ready to send (RTS), clear to send (CTS), data set ready (DSR), and data terminal ready (DTR) to coordinate the transfer of information. It is supported by virtually all personal computers, and is the default protocol for both of the QScreen Controller’s serial ports. The PDQ Board's two serial ports support limited use of generating a parity bit. Because all of the serial I/O routines on the PDQ Board are revectorable, it is very easy to change the serial port in use without modifying any high level code. Typical line voltage levels from the line drivers are a minimum of ±1.5 V to a maximum of about ±6 V. Receiver input sensitivity is ±200 mV. Noise in the range of ±200 mV is essentially blocked due to common-mode noise cancellation. They have Shielding Jacket over the insulation layer to protect against the Electromagnetic Interference and also each pair of wires is twisted together to prevent any current loop formation and thus much better protection against the noise.

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