When the QScreen Controls the Network
본문
The EIA has officially disbanded and the standard is now maintained by the TIA as TIA-485, but engineers and applications guides continue to use the RS-485 designation. The issue also exists in programmable logic controller applications. But I notice that he describes using a (different) RS-485 to USB converter and splicing from the Ethernet cable to the converter, rather than using the converter cable that ships with the charge controller. RS-485, like RS-422, can be made full-duplex by using four wires. It requires minimal wiring and can share the wiring among several seats, reducing weight. RS-485 is also used in building automation as the simple bus wiring and long cable length is ideal for joining remote devices. As a rule of thumb, the speed in bit/s multiplied by the length in metres should not exceed 108. Thus a 50-meter cable should not signal faster than 2 Mbit/s. Although many applications use RS-485 signal levels, the speed, format, and protocol of the data transmission are not specified by RS-485. Currently available high-resistance RS485 inputs allow this number to be expanded to 256.RS485 repeaters are also available which make it possible to increase the number of nodes to several thousands, spanning multiple kilometers.And that with an interface which does not require intelligent network hardware: the implementation on the software side is not much more difficult than with RS232.
For RS232 operation: Install the jumper shunt across the two pins closest to the crystal (the default configuration). When using the default RS485 receivers with an input resistance of 12 kΩ it is possible to connect 32 devices to the network. Maintain as much distance as possible and cross any power cable at a right angle. There are many possible configurations of master/slave networks. There are many different types of serial communication protocols like I2C and SPI which can be easily implemented with Arduino and today we are going to look at another most commonly used protocol called RS485 which is very commonly used in high noise industrial environments to transfer the data over a long distance. For the QScreen, /SS is not used for SPI communication because it is used to control the direction of the RS485 transceiver; you can use any digital I/O line as a /SS signal. RS485 is also used in performance venues to control lights and systems such as the one shown below. In the picture above, the general network topology of RS485 is shown. Receivers on a network (RS485 or RS422) have built in hysteresis (200mV differential required to insure known state). RS-485 supports inexpensive local networks and multidrop communications links, using the same differential signaling over twisted pair as RS-422.
RS-485 and RS-422 can interoperate with certain restrictions. Unloaded driver output differential voltage can be as high as ±6V. The QScreen Controller’s kernel software contains a complete set of high level driver routines for the Serial2 port, and these functions are summarized in the Control-C Glossary. Modbus ASCII messages are framed by a leading colon (":") and trailing newline (CR/LF). RS-485 is used as the physical layer underlying many standard and proprietary automation protocols used to implement industrial control systems, including the most common versions of Modbus and Profibus. It is also used in Digital Command Control (DCC) for model railways. Now select the "Comm" item in the "Settings" menu of the Terminal program, and click on 1200 baud (or whatever baud rate you selected in the command above). For an on, space or logic 0 state, the driver's A terminal is positive relative to the B terminal. For an off, mark or logic 1 state, the driver's A terminal is negative 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.
If A is negative with respect to B, what is rs485 cable the state is binary 1. The reversed polarity (A positive with respect to B) is binary 0. The standard does not assign any logic function to the two states. And now the most important question, how does RS485 function in practice? 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. Grounds between buildings may vary by a small voltage, but with very low impedance and hence the possibility of catastrophic currents - enough to melt signal cables, PCB traces, and transceiver devices. 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. The QVGA Controller’s on-board 12 bit A/D and 8 bit D/A converters communicate with the processor via the SPI.