• 목록
• 답변
• 글쓰기
• 게시판 리스트 옵션
  • 수정
  • 삭제

The most common cable type is Cat 5e-UTP (unshielded twisted pair) which may work over shorter distances in less demanding applications with low EMI noise levels. 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. You can operate the port at any baud rate up to 4800 baud; just specify the rate you want before the BAUD2 command. The actual baud rate produced differs from that requested by a small error owing to rounding of an internal divisor. 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.

In practice, Cat 5 cables have been used successfully in many installations, rs485 cable but there are some concerns. It seems if there is a lot of RFI in the installation, shielded twisted cable can be justified. The cable which I have used in the tutorial is 25m in length. Ideally, the two ends of the cable will have a termination resistor connected across the two wires and two powered resistors to bias the lines apart when the lines are not being driven. The two lowest order bits in the SPCR control register, named SPR1 and SPR0, determine the data exchange frequency expressed in bits per second; this frequency is also known as the baud rate. Each UART implements transmit and receive FIFO buffers to reduce the required frequency of service by the host processor. Rather, the transmitter and receiver must be communicating using a known baud rate, or bit frequency. Shown below is the example of how a character is a transmitter over a UART data line. End of line termination resistor (120 ohm 1/4 watt) to be installed at both ends of network. 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).

At small transmission distances speeds up to 35Mbps can be realized with RS485 although the transmission speed will decrease with distance. Signal High and Lows are measured against the GND level so shifting the GND level will have a disastrous effect on the data transfer. Previously we have also performed MAX485 communication with Arduino and also MAX485 Communication with Raspberry pi, you can also check them out if interested. Most of the low-cost sensors and other modules like GPS, Bluetooth, RFID, ESP8266, etc. which are commonly used with Arduino, Raspberry Pi in the market uses UART TTL based communication because it only requires 2 wires TX(Transmitter) and RX (Receiver). Do note that both transmitter and receiver circuits look identical the only thing that differs is the code written into it. If your application requires RS485, you can use the secondary serial port (serial2) to program and debug your application code using the RS232 protocol, and use the primary serial port (Serial1) for RS485 communications. RS232 could only handle one.

RS422 (differential) was designed for greater distances and higher Baud rates than RS232. It operates on a differential signaling method of measurement rather than voltage measurement wrt GND pin. By polling the Port A pin or by setting up an interrupt service routine, you can configure the QScreen to ignore the SCK input when /SS is high and keep MISO in a high-impedance state so that it does not interfere with the SPI bus. RS-485 is used for low-speed data communications in commercial aircraft cabins' vehicle bus. In this manner, data can be exchanged between the master and each slave on the bus. The master and slave can then exchange data. UART transmitted data is organized into packets. In this tutorial, we are going to learn about the RS485 communication protocol and how to implement it with the two Arduino Nano we have with us and how to use the MAX485 RS485 to UART conversion Module. Two wire telephone cables will not function because in that case the ground signal levels on both sides will be floating. 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.