Two devices are at the ends of the cable, while others are connected somewhere in between. In general, all devices on a network should use the same phase, polarity, and baud rate clock signal. RS485 multi-drop networks are daisy-chained networks with a single cable connecting multiple 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. If you are using the QScreen as a slave device and require the /SS signal for your external SPI hardware, configure one of the Port A pins on the Field Header as an input pin. As the master transmits a byte to an active slave (that is, a slave with its /SS input active low), the master receives a byte from the slave. The GROUND line serves as a common voltage reference for the master and slave. 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 Silence() routine searches the incoming serial characters for a pre-determined keyword (for example, the ascii "name" of this particular slave).

Each of the two channels on the UART Wildcard implements two 16-character FIFOs, one for outgoing characters and one for incoming characters. Because the software UART is interrupt based, competing interrupts that prevent timely servicing of the Serial2 interrupts can cause communications errors on the secondary serial channel. So long as the error between the actual baud rate and that specified is less than 1.5% (or the error between transmitter and receiver is less than 3%) there should be no communication errors. ANC-6090 converts RS232 level signals to RS422 or RS485 differential signals for noise immune communication at 921 Kbaud at distances up to 4000 feet The adapter can also be used for RS232 to TTL/CMOS serial interfacing. USB to RS485 Converter ใช้ต่อกับ USB port ของ PC หรือ Note Book แปลงเป็นสัญญาณ RS485 Communication.

The USB to RS485 Converter is designed to make serial port expansion quick and simple. 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, rs485 cable and configures Serial1 for RS232 operation if the jumper cap is not installed. For Serial2 RS232 operation: Remove the jumper shunt from "2 485En" (J7). For Serial1 RS232 operation: Remove the jumper shunt from "1 485En" (J4). For Serial1 RS485 operation: Install the jumper shunt onto "1 485En" (J4). For Serial2 RS485 operation: Install the jumper shunt onto "2 485En" (J7). 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.

The following table shows the connection diagram for a standard 9-pin serial cable. All of the RS232 signals start with the / (slash, pronounced not) character to indicate that the signals on the serial cable are logically inverted. If your application requires RS485, you can use the secondary serial port (serial2) to program and debug your application code using the RS232 protocol, and use the primary serial port (Serial1) for RS485 communications. The default serial routines used to download programs to the operating system assume that full duplex communications are available, so you cannot use the RS485 protocol to program the controller. It is supported by virtually all personal computers, and is the default protocol for both of the QScreen Controller’s serial ports. To provide a convenient means of attaching two grounds to the serial cable, there are several pins (labeled DGND) on the communications connector that are connected to the controller’s ground plane. Likewise, the terminal’s transmit signal TxD is connected to the QScreen Controller’s receive signal RxD1. 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).