RS232 Uses Inverse Logic; that Is > 커뮤니티 카카오소프트 홈페이지 방문을 환영합니다.

The default serial routines used by the onboard kernel assume that full duplex communications are available, so you cannot use the RS485 protocol to program the controller. Using the primary serial port is easy. Since both channels can operate simultaneously and independently, debugging can be performed while the application program is communicating via its primary channel. 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. If you are running Serial2 at 4800 baud, the rest of your application must be able to function properly using the remaining portion of the CPU time. Thus in Table 9 6 , RTS1 is connected to CTS1, and DSR1 is connected to DTR1 and DCD1 onboard the QScreen Controller using zero ohm shorting resistors. Thus RS485 is the standard protocol of choice when multi-drop communications are required. The RS485 protocol uses differential data signals for improved noise immunity; thus RS485 can communicate over greater distances than RS232. The QScreen Controller’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 symmetrical pin layout of the RJ11 sockets on the Unitronics PLCs allows an easy way of interconnecting the PLCs with both RS232 and RS485 communications. 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. After configuring the SPI system to communicate on a properly connected network of devices, sending and receiving data is as simple as writing and reading a register. The received data byte is accessed by reading SPDR data register. Without termination resistors, signal reflections off the unterminated end of the cable can cause data corruption. 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. A jumper, J3, configures the primary serial port for either RS232 or RS485 operation. 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. The dual communications channels also provide an easy way to link systems that communicate using different serial protocols.

Electrical signaling is balanced, and multipoint systems are supported. These characteristics make RS-485 useful in industrial control systems and similar applications. RESOURCE and the access control functions GET() and RELEASE(). 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. Because all of the serial I/O routines on the QScreen Controller are revectorable, it is very easy to change the serial port in use without modifying any high level code. The Serial 1 port is implemented with the 68HC11's on-chip hardware UART (Universal Asynchronous Receiver/Transmitter). Move the serial cable from the "Serial Port 1" connector to the "Serial Port 2" connector on the QScreen. There are surface mount resistor pads on the QScreen that will allow you to bring out the secondary serial port to the Field Header on pins 5-6 or 7-8 as shown with the parentheses in Table 11-3. Pads are also available to bring out the RS485 signals to the DB9 Serial 1 Connector. If PT is set, rs485 cable all transmitted bytes with a parity bit will have an odd number of total '1' bits. 1 or 2 to specify Serial1 or Serial2, respectively, and clears the appropriate PORTJ bit to place the transceiver in receive mode.

RS485Receive() clears bit PD5 to place the transceiver in receive mode, and RS485Transmit() sets bit PD5 to place the transceiver in transmit mode. The above parity settings will also determine how incoming data is interpreted (whether the most significant bit is considered a parity bit or part of the data being transmitted, and how many bits total to expect in each byte). In this section we will consider the most general and simple configurations. 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 QScreen Controller’s receive signal RxD1. The RS232 protocol specifies the use of two separate grounds, a signal ground and a protective (or "chassis") ground. RS232’s greatest benefit is its universality; practically all personal computers can use this protocol to send and receive serial data. It is supported by virtually all personal computers, and is the default protocol for both of the QScreen Controller’s serial ports.