Understanding Serial Communications > 자유게시판

The symmetrical pin layout of the RJ11 sockets on the Unitronics PLCs allows an easy way of interconnecting the PLCs with both RS232 and RS485 communications. The RS485 interface allows the creation of multipoint networks. RS485 is in its design a different interface from RS232. Each RS232 driver uses inverting logic and implements a single-ended bipolar output voltage (that is, one signal that swings above and below ground). The serial output at the UART idles at the logic high (mark) level. The serial interface is asynchronous, meaning that there is no clock transmitted along with the data. No parity means that there is no parity bit. High (mark) parity means that the parity bit is always logic 1 at the UART, rs485 cable and low (space) parity means that the parity bit is always logic 0 at the UART. An optional parity bit can be specified to enable error detection by the UART. By default, all 720 series key pads come with a standard set of commands which can be used to integrate with existing applications or used to build the metal keypad into new application developments. The EIA once labeled all its standards with the prefix "RS" (Recommended Standard), but the EIA-TIA officially replaced "RS" with "EIA/TIA" to help identify the origin of its standards.

The resulting signal levels on the interface cable connect the local and remote in a manner specified by a standard protocol. Therefore for RS485 communications no crossover cable is used. For RS232a crossover cable is used where pin 1 is connected with pin 6 at the other connector, pin 2 with pin 5, etc. This interconnects the transmit and receive signals of both PLCs, and also the handshaking signals DTR and DSR. In other words, each local UART on the wildcard can both send data to and receive data from a remote UART on the other end of a connecting serial cable. The adapter includes a power supply, 6' serial cable and User's Manual. The string pot was mounted to a fixed surface and its cable attached to the floor panel under monitoring. It finds particular application in the Telecom and Industrial Diesel Generator where remote monitoring is employed. To avoid contention on the RS485 bus, the application software must assure that only one transmitter is enabled at a time. 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.

Rather, the transmitter and receiver must be communicating using a known baud rate, or bit frequency. Bauddesired is an unsigned integer from 1 to 56000, 500000 is the frequency of the UART's internal clock and Round(500000/Bauddesired) is an internal divisor (rounded to the nearest integer). This versatile datalogger proved to be a cost effective solution for handling analog, digital and other types of variables with high resolution and speed and also offered expansion modules. For example, Belden 3105A cable can be specified, but different types of cable with equivalent characteristics can be used. The most widely used protocol is RS232, a full duplex protocol with a single-ended bipolar voltage swing on the serial cable. If handshaking is not necessary, an ordinary 4 wire telephone cable could be used, provided that the pins are cross-connected as shown in the picture below. The normal way to implement this is with a two wire system with differential signal levels.

And this way it's easy for - one reason why they do this is that it makes it easy for the stores to update prices. 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. These factors are discussed in more detail in The UART Wildcard: Modem Handshaking Signals. There are different families of products on the market: instruments which measure a single electrical parameter (voltage, current, frequency, and phase angle cosϕ), generally used in single-phase systems, as instrumentation on the machine, and instruments allowing all the electrical parameters to be measured and displayed, both for the single-phase system and for the three-phase system. Both the local and remote UARTs must be configured for the same communications parameters. 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 3 wires are required for half duplex RS485 communications: a pair of transceive wires and a common ground.