In that case, do not install jumper caps at the jumpers labeled "Term" or "RTerm". 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". Many terminals and PCs, however, do rely on hardware handshaking to determine when the other party (in this case the PDQ Board) is ready to accept data. From the PDQ Board’s point of view, these three signals (/TxD, /RxD, and ground) are the only connections required to perform serial communications. The PDQ Board's two serial ports support limited use of generating a parity bit. 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. 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.

96 screw terminals to let you securely connect your signals and your shields. Similar to Original Bobuino; ATMega1284, RS232 port, FTDI FT232RL USB, SD Card Socket, Screw terminals for 4 serial ports, power, 2 input buttons, 3 switch closures, additional SPI-Dual UART with RS485 interface drivers, 3 additional Status LEDs, Arduino shield compatible. Available with male headers, female headers, or screw terminals. This section also defines the logic states 1 (off) and 0 (on), by the polarity between A and B terminals. It also defines three generator interface points (signal lines); A, B and C. The data is transmitted on A and B. C is a ground reference. The USE.SERIAL2 command means that the operating system’s terminal interface now communicates via Serial2. The Serial Peripheral Interface, SPI, is a fast synchronous serial interface. The BufferToSPI() function implements fast data transfer from a specified buffer in the controller’s memory to an SPI device. 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. If a slave device has already stored a byte into its SPDR register, that byte will be exchanged with the master’s byte.

The PE bit, with mask 0x02, determines whether the most-significant bit in each byte is used as a parity bit. The PT bit, with mask 0x01, determines whether even parity or odd parity is used if parity bit generation is enabled. If your application requires communicating with a device that expects to receive a parity bit, the generation of a parity bit and selection of even or odd parity, and whether there are seven or eight data bits in each byte, is performed by setting or clearing bits in the configuration registers SCI0CR1 for Serial1 and SCI1CR1 for Serial2. Data translation between different machines can be performed with ease, rs485 cable and applications that communicate via the primary serial port can be debugged using the secondary channel. RC termination - In some applications requiring low power you may not want to load the line with 120 Ω resistors at each end. The other end of the cable should be terminated similarly. You aren’t limited to fifty feet of cable like with RS232. Think of RS485 as the younger, faster brother of RS232. For Serial1 RS485 operation: Install the jumper shunt onto "1 485En" (J4).

For Serial1 RS232 operation: Remove the jumper shunt from "1 485En" (J4). For Serial2 RS485 operation: Install the jumper shunt onto "2 485En" (J7). 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. 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. The BAUD routine described at the start of this subsection configures the baud rate of each of the Serial1 and Serial2 channels. A jumper, J3, configures the primary serial port for either RS232 or RS485 operation. The RS232 protocol provides for four handshaking signals called ready to send (RTS), clear to send (CTS), data set ready (DSR), and data terminal ready (DTR) to coordinate the transfer of information. 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.