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The remaining inactive slaves may actively receive, or listen to, data on the communications line, but only one slave at a time can transmit a message. TXSoil can transmit the humidity to a Web server or to a VisualVision's display / concentrator such as DisplayRX or ControlHUB or RXTXeasy GSM - with adjustable interval, remaining for the rest of the time in standby with very low consumption. RC termination - In some applications requiring low power you may not want to load the line with 120 Ω resistors at each end. Thus in the table, /RTS1 is connected to /CTS1, and /DSR1 is connected to /DTR1 and /DCD1 onboard the PDQ Board using zero ohm shorting resistors. By default, the RS485 connections are not brought out to the Docking Panel’s DB-9 Serial1 Connector, although custom placement of zero-ohm surface-mount resistors on the Docking Panel can route the RS485 signals to the DB-9. By default, the RS485 connections are not brought out to the Docking Panel’s DB-9 Serial1 Connector.

There are surface-mount resistor pads on the Docking Panel to bring out the RS485 signals to the DB9 Serial 1 Connector. The end devices are responsible for terminating the cable so that there are no reflections from the cable ends. Resistive termination - If the PDQ Board is at the end of the RS485 cable you can terminate the cable by installing jumper caps at both jumper locations, "Term" and "RTerm". No termination - If the PDQ Board is not an end device, you should not terminate that cable. The one you choose depends on the specific device, or devices you will be connecting to. When PE is cleared (equal to zero), the most-significant bit of each transmitted character will be a data bit. If SPIF is set, reading the received data or initiating a new data transfer automatically clears the SPIF bit. Rather, the transmitter and receiver must be communicating using a known baud rate, or bit frequency. Note that the local and the remote must share a common ground, so a minimum of 3 wires are required for full duplex RS232 communications: a transmit wire, a receive wire, and a common ground.

In this case, cable connections must be made to Serial 1 at pins 5 and 6 of the 10-pin Serial Header or pins 7 and 8 on the 24-pin Field Header. In this case, cable connections may be made to Serial 1 at pins 5 and 6 of the PDQ Board’s 10-pin Serial Header , or pins 5 and 6 of the Docking Panel’s 10-pin right-angle Serial Header. From the PDQ Board’s point of view, these three signals (/TxD, /RxD, and ground) are the only connections required to perform serial communications. 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). We assume that you are now communicating with the PDQ Board via the default Serial1 port at the standard 115200 baud rate. Typing a carriage return at the terminal should now produce the familiar ok response via the Serial2 port. When the keyword name is received by the Silence() routine running in the slave, the slave QScreen Controller executes RS485Transmit() to send an acknowledgment to the master (which should now be listening to the serial bus to accept the acknowledgment).

The QScreen Controller controls the RS485 transceiver with bit 5 of Port D of the processor. 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. The secondary serial port is connected similarly except that the onboard connection of /RTS to /CTS, and /DSR to /DTR are permanent. Enabling RS485 on the Serial2 port is parallel to the process described above. 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. Port to modem communications usually use 300, 1200, 2400, 4800, 9600, 19200, 38400, 57600 and 115200 baud. A modem (modulator/demodulator) provides a way of encoding digital data as a set of audio signals that can be sent over a telephone line. The GROUND line serves as a common voltage reference for the master and slave.

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