A (possibly twisted) pair of wires is used to connect two nodes. A challenge is that Laureate meters use RJ11 jacks, while Laureate LT series transmitters use screw-clamp connectors for three discrete wires. The advantage of using Serial1 for RS485 is that the Serial1 RS485 signals are also available on the Docking Panel, while the Serial2 RS485 signals are available only on the PDQ Board’s Serial Communications Header. The PDQ Board’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 following table shows the connection diagram for a standard 9-pin serial cable. Table 9-6 shows the connection diagram for a standard 9-pin serial cable. Normally, this connection is made at one end of the main cable. Rather, it relies on software handshaking via transmission of XON/XOFF characters (ascii 0x11 and 0x13, respectively) to coordinate data transfer and ensure that information is not lost when one of the communicating parties is busy. In simple terms, it is a method used for transmitting information over serial lines between electronic devices.

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. Move the serial cable from the "Serial Port 1" connector to the "Serial Port 2" connector on the QScreen. Thus in Table 9 6 , RTS1 is connected to CTS1, rs485 cable and DSR1 is connected to DTR1 and DCD1 onboard the QScreen Controller using zero ohm shorting resistors. 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. Likewise, the terminal’s transmit signal /TxD is connected to the PDQ Board’s receive signal /RxD1. This signal synchronizes the exchange of bytes between the QScreen and its peripherals. The master and slave could even exchange ascii QED-Forth commands. The GROUND line serves as a common voltage reference for the master and slave. To create a RS485 bus, stack the RS485 Extension on top of a Master Brick.

Enabling RS485 on the Serial2 port is parallel to the process described above. A jumper labeled "2 485En" (J7) enables RS485 operation on the Serial2 port if the jumper cap is installed, and configures Serial2 for RS232 operation if the jumper cap is not installed. A jumper labeled "1 485En" (J4) enables RS485 operation on the Serial1 port if the jumper cap is installed, and configures Serial1 for RS232 operation if the jumper cap is not installed. In that case, do not install jumper caps at the jumpers labeled "Term" or "RTerm". In this case, cable connections may be made to Serial 2 on either the 10-pin PDQ Board Serial Communications Header, or the Docking Panel’s 10-pin right-angle Serial Header, or the Docking Panel’s Serial2 DB-9 Connector. In that case, when using very long cables you can improve noise immunity and assure a valid idle level when the transceiver is not active by installing bias resistors.

Bias termination - Using resistive termination decreases noise immunity, particularly if the cable is loaded with many devices. 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, or vice-versa depending on the parity checking settings. Not more than one breakout board is required per RS485 line. The ComBoard RTS input line controls the driver enable line so the device only talks when it is its turn. The protocols are described in turn. There are many possible configurations of master/slave networks. Therefore it is possible to use the AVR1284-3U board with 64k, 32k, and 16k microcontrollers to save money. 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.