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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. There are surface-mount resistor pads on the Docking Panel to bring out the RS485 signals to the DB9 Serial 1 Connector. The Serial1 and Serial2 ports have identical communications capabilities, although more of the Serial1 signals (both RS232 and RS485) are made available on the Docking Panels headers and connectors. 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. It also has onboard LEDs to display the current state of the chip i.e. whether the chip is powered or its transmitting or receiving data making it easier to debug and use. Although many applications use RS-485 signal levels, the speed, format, and protocol of the data transmission are not specified by RS-485. The primary and secondary serial communications ports are accessible through the PDQ Board's 10 pin, dual row Communications Header (H2) and through the Docking Panel's 10 pin, right-angle, rs485 cable dual row Communications Header (H1) and individual DB-9 Serial 1 and Serial 2 connectors.

RS232 is by far the most common serial protocol, and is the default protocol for both of the PDQ Board’s serial ports. The RS232 protocol specifies the use of two separate grounds, a signal ground and a protective (or chassis) ground. The local and remote must share a common ground, so all serial cables include at least one ground conductor. These detailed signal descriptions and cable diagrams are presented to provide complete information for those who have special communications requirements and for those who wish to make their own application-specific communications cables. All of the serial ports are supported by pre-coded C-language software drivers that make it easy to exchange data. The master and slave could even exchange ascii QED-Forth commands. When the exchange is complete, the slave can again execute the Silence() routine to disable its transmitter and begin listening for its name. For the QScreen, /SS is not used for SPI communication because it is used to control the direction of the RS485 transceiver; you can use any digital I/O line as a /SS signal. Any of these conditions may generate an interrupt if the SPIE (SPI interrupt enable) bit in the SPCR control register is set.

If the programmer has enabled the local interrupt mask for the SPI, an interrupt is recognized at this point. Note that the local and the remote must share a common ground, so a minimum of 5 wires are required for full duplex RS422 communications: two transmit wires, two receive wires, and a common ground. Both the local and remote UARTs must be configured for the same communications parameters. 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! After a factory cleanup, Serial1 is the default serial port for program development and downloading. The RS485 data direction of Serial1 and Serial2 are controlled by the PJ0 and PJ1 processor pins, respectively. RS485 is another protocol supported by the primary serial port on the PDQ Board. By connecting pairs of these handshaking signals together, the terminal or PC can be made to think that the PDQ Board is always ready to send and receive data. Connecting computers together in multi-drop networks is common in factories and laboratories.

SC, G or reference, the common signal reference ground used by the receiver to measure the A and B voltages. Each RS232 driver uses inverting logic and implements a single-ended bipolar output voltage (that is, one signal that swings above and below ground). If your computer does not have an RS232 serial port, low cost USB-to-RS232 serial cables are available; contact Mosaic Industries for details. Each serial port can be configured for the RS232 or RS485 protocol, and runs at standard baud rates up to 115,200 bits per second. Popular Offer MisolWeather Station With Rs485 Port 4 Wires Cable With Cable Length 10 Meter with FREE Shipping Worldwide Now! The recommended arrangement of the wires is as a connected series of point-to-point nodes, a line or bus. Since it uses a differential line over twisted pair (like EIA-422), it can span relatively large distances (up to 4000 feet or just over 1200 metres). In this project, we have only used a baud rate of 9600 which is well under the maximum transfer speed we can achieve with the MAX-485 Module but this speed is suitable for most of the sensor modules out there and we don’t really need all the maximum speeds while working with Arduino and other development boards unless you are using the cable as an ethernet connection and require all the bandwidth and transfer speed you can get.