RS232 Uses Inverse Logic; that Is > 자유게시판

It is a half duplex protocol, meaning that only one party at a time may transmit data. In the most common multi-drop RS485 protocol, one computer is designated as a master and the rest of the computers or devices on the serial bus are designated as slaves. RS485Receive() to wait for any pending character transmission to complete, then disable the transmitter, and then execute a routine such as Key() to listen to the communications on the serial bus. The Silence() routine searches the incoming serial characters for a pre-determined keyword (for example, the ascii name of this particular slave). When the keyword name is received by the Silence() routine running in the slave, the slave PDQ Board executes RS485Transmit() to send an acknowledgment to the master (which should now be listening to the serial bus to accept the acknowledgment). When the network master wants to talk to this particular slave, it outputs the slave’s ascii name onto the serial bus.

HP is a company that makes and market particular hardware / software for speciallist application. The secondary serial port is implemented by a software UART that controls two pins on PortA. 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 master and slave could even exchange ascii QED-Forth operating system commands. In fact, the program works the same as it did before, but now it is using the secondary serial port instead of the primary port -- and you didn’t even have to recompile the code! If PT is cleared, then all transmitted bytes with a parity bit will have an even number of total '1' bits. If PT is set, all transmitted bytes with a parity bit will have an odd number of total '1' bits. 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). The data bits are also transmitted in reverse order, with the least significant bit transmitted first, after a start bit.

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 Control-C Glossary contains a list of functions that temporarily disable interrupts, and the glossary entries give further information regarding how long interrupts are disabled. Function prototypes for this function and other versatile serial I/O routines are defined in the COMM.H header file, and are described in detail in the Control-C Glossary. In this case, cable connections may be made to Serial 1 on either the 10-pin Serial Communications Header or the Serial 1 Connector. The RS485 connections are not brought out to the Serial 1 Connector. The cable rejected the way which the transceivers of the RS485 is controlled by the PLC, and all the data transceivers is automatic controlled. The diagram below shows a basic RS485 cable for use with the RJ11 socket on Unitronics PLCs.

The PDQ Board controls the Serial1 and Serial2 RS485 transceivers with bits PJ0 and PJ1, respectively, of PORTJ of the processor. RS485Init() configures PORTJ to ensure that bits 0 and 1 are outputs, and disables both RS485 transmitters, leaving the Serial1 and Serial2 RS485 channels in receive mode. The snap switch located on the TSX08PRGCAB programming cable are used to choose a different mode of operation. The cable can communicate with TER interface of TSX Premium (57), TSX Micro (37), TSX Nano (07), TSX Naza (08) Twido PLC, and to realize the procedures to upload, download, surveillance and other function such as multi-point communication of MODBUS. You can use one or both of the PDQ Board’s RS485 links to create such a multi-drop serial network. If you are using the QScreen as a slave device and require the /SS signal for your external SPI hardware, configure one of the Port A pins on the Field Header as an input pin. 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.