For Serial2 RS232 operation: Remove the jumper shunt from "2 485En" (J7). For Serial2 RS485 operation: Install the jumper shunt onto "2 485En" (J7). For Serial1 RS485 operation: Install the jumper shunt onto "1 485En" (J4). For Serial1 RS232 operation: Remove the jumper shunt from "1 485En" (J4). 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". 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 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. In this case, cable connections may be made to Serial 1 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 Serial1 DB-9 Connector. In this case, cable connections may be made to Serial 2 at pins 4 and 10 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.

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. Only one active master may control the network at a time; however, the device that assumes the role of master may change according to an appropriate protocol. Note that the master device outputs the clock synchronization signal SCK to the slave’s SCK which is configured as an input. When the /SS input goes low, the slave (or QScreen in this case) transfers data in response to the SCK clock input that is initiated by the master. The CPHA bit determines whether data is valid on the leading or trailing edge of the clock. The device that initiates a data transfer is the master, and all other devices on the network are slaves. Then reading the data that was received (by reading the SPDR) or initiating a new data transfer (by writing to the SPDR) automatically clears the SPIF flag. The QED-Forth kernel includes pre-coded drivers that configure and control the SPI for maximum speed data transfers. DH 485 is a proprietary communications protocol used by Allen-Bradley in their line of industrial control units.

The SCK pin clocks the serial A/D’s CLK input which causes the A/D’s conversion result to be transferred to the master via the MISO line. Thus, the master has only one input, MISO, which is the slave’s only output. There are a variety of ways the MOSI, MISO, SCK and /SS pins on your QScreen Controller can be connected. The end devices are responsible for terminating the cable so that there are no reflections from the cable ends. Two devices are at the ends of the cable, while others are connected somewhere in between. The PDQ Board's two serial ports support limited use of generating a parity bit. If two bits are received incorrectly, the error will go unnoticed by parity checking. For seven data bits with a parity bit, M would be cleared (equal to zero), and PE would be set in order to make the most-significant bit of a normal eight-bit byte be used by the serial port as a parity bit.

RS-485 is used for low-speed data communications in commercial aircraft cabins' vehicle bus. Multiple receivers may be connected to such a network in a linear, multidrop bus. They should generally not be needed, except if you use long cables, multiple RS485 devices, and resistive termination. RS485 multi-drop networks are daisy-chained networks with a single cable connecting multiple devices. 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. 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. Enabling RS485 on the Serial2 port is parallel to the process described above. On the other hand, the secondary serial port (Serial2) is implemented using hardware pins PA3 (input) and PA4 (output), and is controlled by the associated interrupts IC4/OC5 and OC4, respectively. 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.