Rs485 Cable - Dead or Alive? > 자유게시판

The primary channel’s UART translates the bit-by-bit data on the serial cable into bytes of data that can be interpreted by the QED-Forth Kernel or by your application program. However, verifying correct parity of bytes received with a parity bit is currently not supported. RS423 is another single ended specification with enhanced operation over RS232; however, it has not been widely used in the industry. EIA standards where previously marked with the prefix "RS" to indicate recommended standard; however, the standards are now generally indicated as "EIA" standards to identify the standards organization. We tried to build an organic system so that whoever gets a TXtemp, TXsoil sensor or a bridge for RS232 or ModBus sensors and devices like TXdata can immediately use them without wasting time in configurations (and we also took the opportunity to insert some things into our system some "extra" not foreseen by the standards!). RS422 devices. These networks are often used in a half-duplex mode, where a single master in a system sends a command to one of several "slave" devices on a network.

In this manner, data can be exchanged between the master and each slave on the bus. The GROUND line serves as a common voltage reference for the master and slave. The distinction between master and slave is an important one. The InitSPI() function provides a convenient way to initialize the SPI as the master at a 2MHz baud rate. The actual baud rate produced differs from that requested by a small error owing to rounding of an internal divisor. The UART Wildcard supports any baud rate produced by the above formula. The Electronics Industry Association (EIA) has produced standards for RS485, RS422, RS232, and RS423 that deal with data communications. RS485 meets the requirements for a truly multi-point communications network, and the standard specifies up to 32 drivers and 32 receivers on a single (2-wire) bus. With the introduction of "automatic" repeaters and high-impedance drivers / receivers this "limitation" can be extended to hundreds (or even thousands) of nodes on a network.

The connection between two or more elements (drivers and receivers) should be considered a transmission line if the rise and/or fall time is less than half the time for the signal to travel from the transmitter to the receiver. Since it uses a differential line over twisted pair (like EIA-422), it can span relatively large distances (up to 4000 feet or just over 1200 metres). The specification allows for data transmission from one transmitter to one receiver at relatively slow data rates (up to 20K bits/second) and short distances (up to 50Ft. @ the maximum data rate). Control and monitoring systems: A single pair of rs485 signal cable can connect up to 32 devices, with a signal transmission distance of up to 1200m. Therefore, using rs485 cables is an ideal choice for industrial control and monitoring systems, especially those with large-scale and high dispersion. The RS422 receiver converts the differential signal to the 0 to 5 volt logic signal required by the UART circuitry. The RS232 signals are represented by voltage levels with respect to a system common (power / logic ground).

RS422 (differential) was designed for greater distances and higher Baud rates than RS232. 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). TXSoil can transmit the humidity to a Web server or to a VisualVision's display / concentrator such as DisplayRX or ControlHUB or RXTXeasy GSM - with adjustable interval, remaining for the rest of the time in standby with very low consumption. To avoid contention on the RS485 bus, the application software must assure that only one transmitter is enabled at a time. Systems of this type (4-wire, half-duplex) are often constructed to avoid "data collision" (bus contention) problems on a multi-drop network (more about solving this problem on a two-wire network in a moment). Also, RS485 drivers are able to withstand "data collisions" (bus contention) problems and bus fault conditions. When communicating at high data rates, or over long distances in real world environments, single-ended methods are often inadequate. Electronic data communications between elements will generally fall into two broad categories: single-ended and differential. RS232 (single-ended) was introduced in 1962, and despite rumors for its early demise, has remained widely used through the industry.

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