Understanding Serial Communications > 자유게시판

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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. However, note that the functions that write to EEPROM disable interrupts for 20 msec. Alternatively, the if the SPI interrupts are enabled, the SPI interrupt handler determines what caused the interrupt by reading the SPSR register to see which of the three status bits is set. The Serial1 and Serial2 ports are is supported by the HCS12's dual on-chip hardware UARTs, and do not require interrupts to work properly. 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. You can use one or both of the PDQ Board’s RS485 links to create such a multi-drop serial network. 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. Likewise, the terminal’s transmit signal /TxD is connected to the PDQ Board’s receive signal /RxD1.

We can gain insight into the operation of the RS232 protocol by examining the signal connections used for the primary serial port in the above table. We can gain insight into the operation of the RS232 protocol by examining the signal connections used for the primary serial port in Table 9 6. The transmit and receive data signals carry the messages being communicated between the QScreen Controller and the PC or terminal. Data translation between different machines can be performed with ease, and applications that communicate via the primary serial port can be debugged using the secondary channel. You can implement the slave select lines by configuring Port A pins as outputs. RS232 has numerous handshaking lines (primarily used with modems), and also specifies a communications protocol. In general if you are not connected to a modem the handshaking lines can present a lot of problems if not disabled in software or accounted for in the hardware (loop-back or pulled-up). Two RS485 transceivers are present on the PDQ Board, one for each channel. 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.

Once a character is sent the hardware reverts back into a receive mode in about 1-2 microseconds (at least with R.E. After the slave transmission is complete, the slave puts itself back into receive mode so that the master can transmit additional commands. RS485 extends the common mode range for both drivers and receivers in the "tri-state" mode and with power off. 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. Slave devices use the master in/slave out pin, MISO, for transmitting, and the master out/slave in pin, MOSI, for receiving data. 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.

The UART Wildcard provides two simultaneous communications links, each configurable as RS232, RS485 or RS422. 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. 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. 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. No parity means that there is no parity bit. If PT is cleared, then all transmitted bytes with a parity bit will have an even number of total '1' bits. Even parity means that the bits sum to an even number, and odd parity means that the bits sum to an odd number.

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