Does Rs485 Cable Sometimes Make You feel Silly? > 자유게시판

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The RS485 receiver compares the voltage difference between both lines, instead of the absolute voltage level on a signal line. The difference between the wires’ voltages is what conveys the data. 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. For the transfer of data, the baud rates of both Master and Slave must be between 10% of each other. If you are running Serial2 at 4800 baud, the rest of your application must be able to function properly using the remaining portion of the CPU time. Thus, as a rough approximation, operating at 4800 baud full duplex requires about 40 to 50% of the 6811's CPU time (that is, an average of approximately 40 to 50 µs service time every 100 µs). 1200 is the baud rate that you choose; you can specify any standard baud rate up to 4800 baud. It is not a standard Communication protocol, but it is a physical circuit with which you can transmit and receive serial data with other peripherals. The circuit diagram given above explains how the onboard MAX485 IC is connected to various components and provide 0.1-inch standard spacing headers to be used with breadboard if you like.

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. 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). This works well and prevents the existence of ground loops, a common source of communication problems. A ground connection is also necessary to ensure that the communicating devices have a common voltage reference.

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. It operates on a differential signaling method of measurement rather than voltage measurement wrt GND pin. Signal High and Lows are measured against the GND level so shifting the GND level will have a disastrous effect on the data transfer. 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. In practice, Cat 5 cables have been used successfully in many installations, but there are some concerns. Previously we have also performed MAX485 communication with Arduino and also MAX485 Communication with Raspberry pi, you can also check them out if interested. It works on half-duplex communication to implement the function of converting the TTL level into RS-485 level which means it can either transmit or receive at any time, not both, it can achieve a maximum transmission rate of 2.5Mbps. MAX485 transceiver draws a supply current of between 120μA and 500μA under the unloaded or fully loaded conditions when the driver is disabled.

100 ohms, Cat 5 cables almost meets the electrical requirements for RS-485 cables. 24 AWG solid wires, which are typically used in Cat 5 cables, can break easily when connected to a screw terminal block, which does not provide any strain relief. There are many categories of Ethernet cables we can use like CAT-4, CAT-5, CAT-5E, CAT-6, CAT-6A, etc. In our tutorial, we are going to use CAT-6E cable which has 4 twisted pairs of 24AWG wires and can support up to 600MHz. It is terminated at both ends by an RJ45 connector. The end devices are responsible for terminating the cable so that there are no reflections from the cable ends. End of line termination resistor (120 ohm 1/4 watt) to be installed at both ends of network. Plugging the device into the USB Port, it is automatically detected and installed. All communication cabling to be installed in a daisy chain configuration, no T’s are permitted.

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