12VDC / Minimum 400 MA > 자유게시판

RS232 is by far the most common protocol. The local and remote must share a common ground, so all serial cables include at least one ground conductor. 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. The words port and channel are used interchangeably to refer to a serial communications link. Confirm serial port parameters such as baud rate, data bits, and stop bits: Baud rate should be configured according to the connected RS485 device, commonly used rates are 9600 and 115200; Refer to the device manual or contact RS485 device technical support for configuration, especially if set to Modbus mode, confirm if the function code matches. A UART is a Universal Asynchronous Receiver/Transmitter that converts parallel data from the host processor (any Mosaic controller) into a serial data stream. The QScreen Controller controls the RS485 transceiver with bit 5 of Port D of the processor. The PDQ Board controls the Serial1 and Serial2 RS485 transceivers with bits PJ0 and PJ1, respectively, of PORTJ of the processor. With this boards, a CBL03 lines with RJ11 connectors can branch out to support an RS485 line consisting of three discrete wires.

A challenge is that Laureate meters use RJ11 jacks, while Laureate LT series transmitters use screw-clamp connectors for three discrete wires. We’ll use code from the GETSTART.C program. 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! 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. If you're sitting in the office right now, and you look to see your thermostat, there's usually RS-485 transceivers connecting that from there to basically the control unit in the building. See the following example for switching among the various parity modes on Serial1. 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. Twisted pair structure: Rs485 anti-interference cable has a twisted pair conductor structure. In RS485 mode, the RS422 transmit and receive pairs are shorted together with a pair of onboard jumpers as explained in the UART Wildcard Hardware: RS485 Jumpers section below.

If you use a twisted pair cable, make sure to use the same twisted pair for A and B, but use another twisted pair for GND. In general, all devices on a network should use the same phase, polarity, and baud rate clock signal. Note that the master device outputs the clock synchronization signal SCK to the slave’s SCK which is configured as an input. The advantage of a balanced signal is the greater immunity to noise. This allows for basic error detection, in that if noise on the transmission line causes one bit to be received incorrectly, either received as a '0' when transmitted as a '1' or vice-versa, the error would be detected due to the count of '1' bits in the byte being odd when it is expected to be even, rs485 cable or vice-versa depending on the parity checking settings. In either of these cases, a source of noise that caused one bit to be received incorrectly would invalidate the received byte, since the total number of '1' bits would be odd rather than even.

Data translation between different machines can be performed with ease, and applications that communicate via the one serial port can be debugged using the other serial channel. 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). Serial1 port the default startup serial link. 1 or 2 to specify Serial1 or Serial2, respectively, and clears the appropriate PORTJ bit to place the transceiver in receive mode. 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. When this bit is high, the transceiver is in transmit mode.