이름 : Zella
이메일 : zellahanks@hotmail.co.uk
연락처 :
예식일 : All About Rs485 Cable
문의내용:

To provide a convenient means of attaching two grounds to the serial cable, there are several pins (labeled DGND) on the communications connector that are connected to the controller’s ground plane. Chassis and signal grounds are connected together to the digital ground (DGND) signal. Although the RS232 protocol specifies functions for as many as 25 pins, each communications channel requires only three for simple serial interfaces: /TxD1 (transmit data), /RxD1 (receive data), and DGND (digital ground). Likewise, the terminal’s transmit signal /TxD is connected to the PDQ Board’s receive signal /RxD1. The PDQ Board’s transmit data signal /TxD1 (pin 2 on the 9-pin serial connector) is connected to the terminal’s receive data signal /RxD (pin 2 on its 9-pin connector). 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. 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.

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. RS232 allows both communicating parties to transmit and receive data at the same time; this is referred to as full duplex communications. From the PDQ Board’s point of view, these three signals (/TxD, /RxD, and ground) are the only connections required to perform serial communications. The PDQ Board does not differentiate between these. Many terminals and PCs, however, do rely on hardware handshaking to determine when the other party (in this case the PDQ Board) is ready to accept data. 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. The Serial ports are implemented by the dual on-chip hardware UARTs (Universal Asynchronous Receiver/Transmitters) on the Freescale 9S12 (HCS12) microcontroller. A UART is a Universal Asynchronous Receiver/Transmitter that converts parallel data from the host processor (any Mosaic controller) into a serial data stream. RS232 uses inverse logic; that is, a positive bit at the 68HC11 UART is inverted by the onboard RS232 driver chip and appears as a negative signal on the serial cable.

The following table shows the connection diagram for a standard 9-pin serial cable. 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. RS232 uses inverse logic; that is, a positive bit at the HCS12 UART is inverted by the onboard RS232 driver chip and appears as a negative signal on the serial cable. 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. RS232’s greatest benefit is its universality; most personal computers can use this protocol to send and receive serial data. If your application requires RS485, use the primary serial port (serial1) for RS485 communications, and use the secondary serial port (Serial 2) to program and debug your application code using the RS232 protocol.

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. 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. 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, rs485 cable or nodes. In the simplest scheme, all RS485 transceivers come up in receive mode when the interface is initialized, and each transceiver node has a unique address known to it and the master. The master and slave can then exchange data. Slave devices use the master in/slave out pin, MISO, for transmitting, and the master out/slave in pin, MOSI, for receiving data. The one you choose depends on the specific device, or devices you will be connecting to.