Eliminate RS485 Standard Once and For All > 자유게시판

One to two logic-high stop bits mark the end of a character. 0.2V the receivers output switches to a 1 and when the voltage goes below -0.2V the receivers output switches to a 0. (or vice versa if there is inversion on the receiver) Since the last bit from a UART will be the stop bit (1), then the transmitter is turned off (the differential voltage goes to 0V, but not having gone less than -0.2V), this should leave the receiver with a 1 being output to the receiving UART. This standard specifies the electrical characteristics of a single transmitter and up to ten receivers on a single pair of wires. Note that the local and the remote must share a common ground, so a minimum of 3 wires are required for half duplex RS485 communications: a pair of transceive wires and a common ground. Note that the local and the remote must share a common ground, so a minimum of 3 wires are required for full duplex RS232 communications: a transmit wire, a receive wire, and a common ground. Note that the local and the remote must share a common ground, so a minimum of 5 wires are required for full duplex RS422 communications: two transmit wires, two receive wires, and a common ground.

Even though the logic function of the generator and receiver are not defined by RS-485, it makes sense to many engineers to have a binary 1 appear on the RS-485 wires when a binary 1 is being transmitted. Forcing the wires to the idle condition when no driver is active is the most common reason to need biasing on the network. It is optimal for outdoor use cases that need reliable data collected over years. The UART Wildcard implements these optional RS232 modem handshaking signals on channel 1. The handshaking signals can be disabled and/or ignored by applications that do not need them. This is, because on the other interfaces the communication channel is shared by multiple receivers and-in the case of RS485-by multiple senders. Multiple Drivers, Multiple Receivers: RS-485 standard supports multiple drivers and receivers on the same communication bus. RS422. RS422 is also specified for multi-drop (party-line) applications where only one driver is connected to, and transmits on, a "bus" of up to 10 receivers.

The RS422 driver and receiver use separate differential conductor pairs on the serial cables, enabling full duplex communications. Serial data is shifted out least-significant-bit first. Most modems communicate using RS232 and a set of hardware handshaking signals used to regulate data flow. Because differential signals have inherently better signal-to-noise properties, reliable RS422 communications can be sent over much longer distances compared to RS232. The receiver is able to respond to differential signal levels of 200mV over the common mode range. A modem (modulator/demodulator) provides a way of encoding digital data as a set of audio signals that can be sent over a telephone line. If the cable doesn't have its nominal impedance stated, it's not per definition intended for high-performance data communications - but if it's at least shielded, it'll probably work just fine in a number of RS485 applications. Even parity means that the bits sum to an even number, and odd parity means that the bits sum to an odd number. A logic-low start bit marks the start of a character, followed by 5 to 8 data bits per character.

Articles, application notes, RS485 standard even data sheets from semiconductor manufacturers discuss both the data rate and line length limits in RS-485. The UART Wildcard supports any baud rate produced by the above formula. The actual baud rate produced differs from that requested by a small error owing to rounding of an internal divisor. So long as the error between the actual baud rate and that specified is less than 1.5% (or the error between transmitter and receiver is less than 3%) there should be no communication errors. An optional parity bit can be specified to enable error detection by the UART. High (mark) parity means that the parity bit is always logic 1 at the UART, and low (space) parity means that the parity bit is always logic 0 at the UART. At the UART, a logic high (5 volts) is called a mark, and a logic low (0 volts) is called a space. A break sequence forces the serial output to a logic low (space) at the UART. But, since one of outputs goes high when the input goes high, it is often called the "non-inverting" output.