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예식일 : How To turn Rs485 Cable Into Success
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SPIE is a local interrupt mask that allows an interrupt to be recognized when an SPI data transfer has completed, or if a write collision or mode fault is detected. Rather, it relies on software handshaking via transmission of XON/XOFF characters to coordinate data transfer and ensure that information is not lost when one of the communicating parties is busy. The distinction between master and slave is an important one. This detects the presence of more than one master on the SPI bus. It receives bytes sent by a slave device via the "master in/slave out" pin, MISO. The status of a device as master or slave determines how the various pins must be configured. In this case, cable connections must be made to Serial 1 at pins 5 and 6 of the 10-pin Serial Header or pins 7 and 8 on the 24-pin Field Header. The pinout of the QScreen’s Serial Header (H5), QScreen’s Field Header (H3), and the Serial Connectors are shown in the following tables. If you have already downloaded the program, you are ready to go. The RS232 protocol provides for four handshaking signals called ready to send (RTS), clear to send (CTS), data set ready (DSR), and data terminal ready (DTR) to coordinate the transfer of information.

The primary serial port, Serial1, is supported by the 68HC11's on-chip hardware UART (sometimes called a USART), and does not require interrupts to work properly. High (mark) parity means that the parity bit is always logic 1 at the UART, and low (space) parity means that the parity bit is always logic 0 at the UART. The standard C serial I/O routines such as printf(), scanf(), putchar(), and getchar() give you high level access to the serial ports. RESOURCE and the access control functions GET() and RELEASE(). It controls the serial-to-parallel and parallel-to-serial conversion and performs all of the timing functions necessary for asynchronous serial communications. The RS422 driver and receiver use separate differential conductor pairs on the serial cables, enabling full duplex communications. By connecting pairs of these handshaking signals together, the terminal or PC can be made to think that the QScreen Controller is always ready to send and receive data. Many terminals and PCs, however, do rely on hardware handshaking to determine when the other party (in this case the QScreen Controller) is ready to accept data. While these signals provide a data path, they do not provide hardware handshaking that allows the two communicating parties to let each other know when they are ready to send or receive data.

From the QScreen Controller’s point of view, these three signals (TxD, RxD, and ground) are the only connections required to perform serial communications. Likewise, the terminal’s transmit signal TxD is connected to the QScreen Controller’s receive signal RxD1. Serial 2 is implemented by a software UART in the controller’s QED-Forth Kernel that uses two of the processor’s PortA I/O pins to generate a serial communications channel. The secondary serial port is implemented by a software UART that controls two pins on PortA. The arrows in the diagram point to pins configured as inputs, and originate from output pins. The SCK (serial clock) pin is a configurable synchronous data clock output. Remember that the /SS is active low so to select a device you need to set the pin low; otherwise the pin should idle high. By polling the Port A pin or by setting up an interrupt service routine, you can configure the QScreen to ignore the SCK input when /SS is high and keep MISO in a high-impedance state so that it does not interfere with the SPI bus.

As the master transmits a byte to an active slave (that is, a slave with its /SS input active low), the master receives a byte from the slave. The master can instruct a single slave to go into transmit mode, and then the master can put itself into receive mode, thereby allowing the master to retrieve data from the slave. When the exchange is complete, the slave can again execute the Silence() routine to disable its transmitter and begin listening for its name. A single master can broadcast commands to all the slaves, and can direct commands to an individual slave using its unique address. Most modems communicate using RS232 and a set of hardware handshaking signals used to regulate data flow. Newer protocols include the full duplex RS422 and the half duplex RS485 protocols, each of which drives differential 0 to 5 volt signals on the serial cable. The protocols are described in turn. The primary and secondary serial communications ports are accessible through the QScreen's 10 pin, dual row Serial Header (H5) which is typically not installed, the 24 pin, dual row Field Header (H3), and through the individual DB-9 Serial 1 and Serial 2 connectors. 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.

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