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If your application requires communicating with a device that expects to receive a parity bit, the generation of a parity bit and selection of even or odd parity, and whether there are seven or eight data bits in each byte, is performed by setting or clearing bits in the configuration registers SCI0CR1 for Serial1 and SCI1CR1 for Serial2. If your application requires use of the secondary serial port as well as other interrupt routines, the key is to keep the interrupt service routines short and fast. Before running the program, let’s switch to the secondary serial port. All of the RS232 signals start with the / (slash, pronounced not) character to indicate that the signals on the serial cable are logically inverted. Each packet contains 1 start bit, 5 to 9 data bits (depending on the UART), an optional parity bit, and 1 or 2 stop bits. UART is an Asynchronous transmission device hence there is no clock signal to sync the data between the two devices instead it uses start and stop bits at the start and end of each data packet respectively to mark the extremities of the data being transferred.

The BAUD routine described at the start of this subsection configures the baud rate of each of the Serial1 and Serial2 channels. 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. In this project, we have only used a baud rate of 9600 which is well under the maximum transfer speed we can achieve with the MAX-485 Module but this speed is suitable for most of the sensor modules out there and we don’t really need all the maximum speeds while working with Arduino and other development boards unless you are using the cable as an ethernet connection and require all the bandwidth and transfer speed you can get. At small transmission distances speeds up to 35Mbps can be realized with RS485 although the transmission speed will decrease with distance. The capacitance is close to 12.5 pF/foot but there is a small impedance mismatch (100 ohms for Cat 5, 120 ohms for RS-485).

We have been using Microcontroller Development Boards like Arduino, Raspberry Pi, NodeMCU, ESP8266, MSP430, etc. for a long time now in our small projects where most of the times distance between the sensors and board is not more than few centimeters at max and at these distances, the communication between the different sensor modules, relays, actuators, and controllers can be easily done over simple jumper wires without us being worried about the signal distortion in the medium and the Electrical noises creeping into it. But if you are building a control system with these development boards over a distance greater than 10 to 15 meters, then you should take the noise and signal power into consideration because if you want your system to work reliably, then you cannot afford to lose the data while transferring. We will send some data from the transmitter side over the cable from the Nano which is converted to RS485 signals via MAX RS485 Module working in Master Mode.

RS485Init() configures PORTJ to ensure that bits 0 and 1 are outputs, and disables both RS485 transmitters, leaving the Serial1 and Serial2 RS485 channels in receive mode. On the other hand, the secondary serial port (Serial2) is implemented using hardware pins PA3 (input) and PA4 (output), and is controlled by the associated interrupts IC4/OC5 and OC4, respectively. RS485 is another protocol supported by the primary serial port on the QScreen Controller. Popular Offer MisolWeather Station With Rs485 Port 4 Wires Cable With Cable Length 10 Meter with FREE Shipping Worldwide Now! The cable which I have used in the tutorial is 25m in length. Signal High and Lows are measured against the GND level so shifting the GND level will have a disastrous effect on the data transfer. The USB-RS485-WE cable was designed to be used with Alliance Sensors Group LVDT Signal Conditioners and a laptop/computer. 2 Alphanumeric LCD, and MAX485 UART to RS485 converter IC connected to each end of an Ethernet Cat-6E cable via an RJ45 connector. This UART-RS485 Converter module has an on-board MAX485 chip which is a low-power and slew-rate-limited transceiver used for RS-485 communication. RS485Receive() clears bit PD5 to place the transceiver in receive mode, rs485 cable and RS485Transmit() sets bit PD5 to place the transceiver in transmit mode.