이름 : Tasha
이메일 : tashagoffage@yahoo.com
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예식일 : Rs485 Cable And Different Products
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The InitSPI() function provides a convenient way to initialize the SPI as the master at a 2MHz baud rate. The USB-RS485-PCBA converter provides a USB to RS485 serial interface with a simple USB type A connector and PCB for easy integration into a design or as the basis of a converter cable. USB Serial - The ANC-6204 multi-interface USB adapter provides RS232, RS422/485 or TTL/CMOS in one converter. One uses the data lines for 10/100 Ethernet, so that there are still 2 unused pairs in that cable. Without termination resistors, signal reflections off the unterminated end of the cable can cause data corruption. In order to avoid signal reflections, a 120 Ohm termination resistance must be fitted on each end of the main cable. Ideally, the two ends of the cable will have a termination resistor connected across the two wires. RS-485, like RS-422, can be made full-duplex by using four wires. In contrast to RS-422, which has a driver circuit which cannot be switched off, RS-485 drivers use three-state logic allowing individual transmitters to be deactivated. If a star configuration is unavoidable, special RS-485 repeaters are available which bidirectionally listen for data on each span and then retransmit the data onto all other spans.

It also defines three generator interface points (signal lines); A, B and C. The data is transmitted on A and B. C is a ground reference. 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. Maximum Cable Length 50 FT. Using a repeater, the main cable is divided into different segments, rs485 cable each of which can be up to 700 m in length and connect 32 devices (this number includes the repeaters). If PT is set, all transmitted bytes with a parity bit will have an odd number of total '1' bits. This way, the lines will be biased to known voltages and nodes will not interpret the noise from undriven lines as actual data; without biasing resistors, the data lines float in such a way that electrical noise sensitivity is greatest when all device stations are silent or unpowered. Signal High and Lows are measured against the GND level so shifting the GND level will have a disastrous effect on the data transfer. I would highly discourage the use of extra signal pins in the connectors for "cable connected" checking that do not meet the same specs as the RS485 signalling signals.

Star and ring topologies are not recommended because of signal reflections or excessively low or high termination impedance. This allows RS-485 to implement linear bus topologies using only two wires. By using repeaters very large RS-485 networks can be formed. RS232’s greatest benefit is its universality; practically all personal computers can use this protocol to send and receive serial data. UART interface support for 7 or 8 data bits, 1 or 2 stop bits and odd / even / mark / space / no parity. The PT bit, with mask 0x01, determines whether even parity or odd parity is used if parity bit generation is enabled. The Serial1 and Serial2 ports have identical communications capabilities, although more of the Serial1 signals (both RS232 and RS485) are made available on the Docking Panels headers and connectors. Typing a carriage return at the terminal should now produce the familiar ok response via the Serial2 port. 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. RS-485 signals are used in a wide range of computer and automation systems. Electrical signaling is balanced, and multipoint systems are supported.

The termination also includes pull up and pull down resistors to establish fail-safe bias for each data wire for the case when the lines are not being driven by any device. Termination resistors also reduce electrical noise sensitivity due to the lower impedance. Sig- lines are twisted as twisting nullify the effect of electromagnetic noise induced in a cable and provide a much better immunity against the noise which allows the RS485 to transmit the data up to 1200m of range. The primary serial channel can operate at standard speeds up to 19200 baud and can be configured for either RS232 (the default) or RS485 operation. If your application requires RS485, use the primary serial port (serial1) for RS485 communications, and use the secondary serial port (Serial 2) to program and debug your application code using the RS232 protocol. Although the RS232 protocol specifies functions for as many as 25 pins, each communications channel requires only three for simple serial interfaces: /TxD1 (transmit data), /RxD1 (receive data), and DGND (digital ground). RS-485 only specifies the electrical characteristics of the generator and the receiver: the physical layer.