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As described below, the RS485Transmit() function controls the RS485 data direction of each serial port. Each UART (sometimes referred to as a "USART") controls the serial-to-parallel and parallel-to-serial conversion and performs all of the timing functions necessary for one asynchronous serial communications link. Typically one device (node) is addressed by the host computer and a response is received from that device. If your computer does not have an RS232 serial port, low cost USB-to-RS232 serial cables are available; contact Mosaic Industries for details. The PDQ Single Board Computer (SBC) has two asynchronous serial communications ports named Serial1 and Serial2. The flexibility and power of the 68HC11’s serial peripheral interface supports high speed communication between the 68HC11 and other synchronous serial devices. Of the processor’s three synchronous SPI (Serial Peripheral Interface) ports, two are available for inter-processor communications on multi-processor systems, and the third is brought out to the Wildcard expansion bus.

This page describes the serial ports and how to use them for instrument control and automation applications. Because a single pair of conductors is used for both transmission and reception, RS485 is useful for multi-drop applications in which a master communicates with multiple slave serial devices, or nodes. Differential data transmission (balanced differential signal) offers superior performance in most applications. RS422 (differential) was designed for greater distances and higher Baud rates than RS232. The RS422 receiver converts the differential signal to the 0 to 5 volt logic signal required by the UART circuitry. The RS232 driver and receiver use separate conductors on the serial cables, enabling full duplex communications. Receiver Input Resistance (Ohms), (1 Standard Load for RS485) 3k to 7k 4k min. The Serial 1 and Serial2 ports can be configured for either RS-232 or RS-485 communications at standard baud rates up to 115200 bits per second. RS232 is by far the most common serial protocol, rs485 cable and is the default protocol for both of the PDQ Board’s serial ports. RS485 is another protocol supported by the primary serial port on the QScreen Controller. RS485 is another protocol supported by the primary serial port on the PDQ Board. The QScreen allows the details of the synchronous communications protocol to be customized for compatibility with a variety of peripherals.

This signal synchronizes the exchange of bytes between the QScreen and its peripherals. 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). After a factory cleanup, Serial1 is the default serial port for program development and downloading. The default baud rate after a factory cleanup is 115200 baud. 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. Having a second serial port is also handy for system debugging. 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. Each device has a communication port with two terminals, which are indicated for the sake of convenience as A and B. In these two terminals the communication cable is connected so that all the devices that take part in the communication are connected in parallel.

The adapter comes standard with a 10-foot power cable and two parallel 4 pin Molex RS-485 connectors. These 9-pin standard DB-9 serial connectors are located on the back of the Docking Panel. Once a character is sent the hardware reverts back into a receive mode in about 1-2 microseconds (at least with R.E. The Serial ports are implemented by the dual on-chip hardware UARTs (Universal Asynchronous Receiver/Transmitters) on the Freescale 9S12 (HCS12) microcontroller. The hardware detects the start-bit of the transmission and automatically enables (on the fly) the RS485 transmitter. Any number of characters can be sent, and the transmitter will automatically re-trigger with each new character (or in many cases a "bit-oriented" timing scheme is used in conjunction with network biasing for fully automatic operation, including any Baud rate and/or any communications specification, eg. 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.