• 목록
• 답변
• 글쓰기
• 게시판 리스트 옵션
  • 수정
  • 삭제

In the most common multi-drop RS-485 protocol, one computer is designated as a "master" and the rest of the computers or devices on the serial bus are designated as "slaves". RS485 multi-drop networks are daisy-chained networks with a single cable connecting multiple devices. They should generally not be needed, except if you use long cables, multiple RS485 devices, and resistive termination. Consult the data sheets for any peripheral devices that you are interfacing to the SPI and, if a different configuration is needed, follow the instructions below to set up the appropriate SPI data transfer protocol. The SPIF is set when a data transfer is complete, and is cleared by a read of the SPSR status register, followed by a read or write to the SPDR data register. 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. All of the serial ports are supported by pre-coded C-language software drivers that make it easy to exchange data. Rather, it relies on software handshaking via transmission of XON/XOFF characters (ascii 0x11 and 0x13, respectively) to coordinate data transfer and ensure that information is not lost when one of the communicating parties is busy.

This detects the presence of more than one master on the SPI bus. When the network master wants to talk to this particular slave, it outputs the slave’s ascii name onto the serial bus. Of the processor’s three synchronous SPI (Serial Peripheral Interface) ports, two are available for inter-processor communications on multi-processor systems, rs485 cable and the third is brought out to the Wildcard expansion bus. The PDQ Single Board Computer (SBC) has two asynchronous serial communications ports named Serial1 and Serial2. The PDQ Board does not differentiate between these. The pinout of the PDQ Board’s Communications Header (H2), Docking Panel’s Communications Header (H1), and the Docking Panel’s Communications DB-9 Connectors are shown in the following tables. In this case, cable connections may be made to Serial 2 at pins 4 and 10 of the PDQ Board’s 10-pin Serial Header, or pins 5 and 6 of the Docking Panel’s 10-pin right-angle Serial Header. RC termination - In some applications requiring low power you may not want to load the line with 120 Ω resistors at each end. In this case, cable connections may be made to Serial 1 on either the 10-pin Serial Communications Header or the Serial 1 Connector.

All of the RS232 signals start with the / (slash, pronounced not) character to indicate that the signals on the serial cable are logically inverted. The Serial1 and Serial2 ports have identical communications capabilities, although more of the Serial1 signals (both RS232 and RS485) are made available on the Docking Panels headers and connectors. It is NOT necessary to introduce long delays in a network to avoid "data collisions." Because delays are NOT required, networks can be constructed, that will utilize the data communications bandwidth with up to 100% through put. 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. 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. Having a second serial port is also handy for system debugging. 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.

If your application requires RS485, you can use the secondary serial port (serial2) to program and debug your application code using the RS232 protocol, and use the primary serial port (Serial1) for RS485 communications. The terminal program communicates with the PDQ Board via this serial port. The transmit and receive data signals carry the messages being communicated between the PDQ Board and the PC or terminal. Contact Mosaic if you require RS485 signals to be routed to the DB-9 Connector. If your computer does not have an RS232 serial port, low cost USB-to-RS232 serial cables are available; contact Mosaic Industries for details. In that case, when using very long cables you can improve noise immunity and assure a valid idle level when the transceiver is not active by installing bias resistors. The local and remote must share a common ground, so all serial cables include at least one ground conductor. Two RS485 transceivers are present on the PDQ Board, one for each channel. This allows for basic error detection, in that if noise on the transmission line causes one bit to be received incorrectly, either received as a '0' when transmitted as a '1' or vice-versa, the error would be detected due to the count of '1' bits in the byte being odd when it is expected to be even, or vice-versa depending on the parity checking settings.