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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). RS423 is another single ended specification with enhanced operation over RS232; however, rs485 cable it has not been widely used in the industry. The PDQ Single Board Computer (SBC) has two asynchronous serial communications ports named Serial1 and Serial2. In the most common multi-drop RS485 protocol, one computer is designated as a master and the rest of the computers or devices on the serial bus are designated as slaves. Typically one device (node) is addressed by the host computer and a response is received from that device. The master initiates a communications request to a "slave node" by addressing that unit. RTS (Request to send) does have some utility in certain applications. These detailed signal descriptions and cable diagrams are presented to provide complete information for those who have special communications requirements and for those who wish to make their own application-specific communications cables. Differential data transmission (balanced differential signal) offers superior performance in most applications. The hardware detects the start-bit of the transmission and automatically enables (on the fly) the RS485 transmitter.

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. 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. While a multi-drop "type" application has many desirable advantages, RS422 devices cannot be used to construct a truly multi-point network. Since both channels can operate simultaneously and independently, serial debugging can be performed while the application program is communicating via its primary channel. In a finished instrument, either or both channels can be used to communicate with other serial devices, or with other computers and/or terminals using RS232 or RS485. Standards have been developed to insure compatibility between units provided by different manufacturers, and to allow for reasonable success in transferring data over specified distances and/or data rates. To solve the "data collision" problem often present in multi-drop networks hardware units (converters, repeaters, micro-processor controls) can be constructed to remain in a receive mode until they are ready to transmit data.

LCD displays can be connected using 1x16, 2x7 or 2x8 connectors. Most modems communicate using RS232 and a set of hardware handshaking signals used to regulate data flow. The Serial ports are implemented by the dual on-chip hardware UARTs (Universal Asynchronous Receiver/Transmitters) on the Freescale 9S12 (HCS12) microcontroller. 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. Single master systems (many other communications schemes are available) offer a straight forward and simple means of avoiding "data collisions" in a typical 2-wire, half-duplex, multi-drop system. RS485 multi-drop networks are daisy-chained networks with a single cable connecting multiple devices. Maximum Cable Length 50 FT. The maximum sustainable baud rate on the secondary serial port is 4800 baud. If you do this now, remember to move the QScreen Controller’s serial connector back to Serial Port 1, and to change the terminal’s baud rate back to 19200 baud using the "Comm" item under the terminal’s "Settings" menu. 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.

These protocols are summarized on this page, but for more information regarding their data formats and their use for simplex or multi-drop serial lines, consult Understanding Serial Communications (but keep in mind that that page is directed to the use of the UART Wildcard, so it uses different driver functions). The AVR1284-3U board uses removable UART interfaces called ComBoards. In this case, cable connections may be made to Serial 1 on either the 10-pin PDQ Board Serial Communications Header, or the Docking Panel’s 10-pin right-angle Serial Header, or the Docking Panel’s Serial1 DB-9 Connector. This 6 ft long cable comes with a USB connector on one end and the red and yellow tipped plugs and does not require a driver if used with Windows 7 or later versions. They translate the bit-by-bit data on the serial cable into bytes of data that can be interpreted by the operating system or by your application program. Each serial port can be configured for the RS232 or RS485 protocol, and runs at standard baud rates up to 115,200 bits per second. For seven data bits with a parity bit, M would be cleared (equal to zero), and PE would be set in order to make the most-significant bit of a normal eight-bit byte be used by the serial port as a parity bit.