If it doesn’t, confirm that the terminal’s baud rate is correct by selecting the Comm item in the Settings menu of the Mosaic Terminal program, and click on 115200 baud. Once the project is open, click Build→ Build, and after the compilation is done, enter the Mosaic Terminal by clicking Tools→ Mosaic Terminal and use the Send File menu item to send GETSTART.DLF to the PDQ Board. 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". Bias termination - Using resistive termination decreases noise immunity, particularly if the cable is loaded with many devices. The one you choose depends on the specific device, or devices you will be connecting to. No termination - If the PDQ Board is not an end device, you should not terminate that cable. They should generally not be needed, except if you use long cables, multiple RS485 devices, and resistive termination.

RC termination - In some applications requiring low power you may not want to load the line with 120 Ω resistors at each end. In that case you may terminate the lines with a series RC network comprising a 0.1 μF capacitor in series with a 120 Ω resistor. That places a 120 Ω resistor across the RS485 differential line at the driver chip. 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. DH 485 is a proprietary communications protocol used by Allen-Bradley in their line of industrial control units. Thus RS485 is the standard protocol of choice when multi-drop communications are required. We assume that you are now communicating with the PDQ Board via the default Serial1 port at the standard 115200 baud rate.

The resulting signal levels on the interface cable connect the local and remote in a manner specified by a standard protocol. The USE.SERIAL2 command means that the operating system’s terminal interface now communicates via Serial2. In the simplest scheme, all RS485 transceivers come up in receive mode when the interface is initialized, and each transceiver node has a unique address known to it and the master. Slave devices use the master in/slave out pin, MISO, for transmitting, and the master out/slave in pin, MOSI, for receiving data. When PE is cleared (equal to zero), the most-significant bit of each transmitted character will be a data bit. The PE bit, with mask 0x02, determines whether the most-significant bit in each byte is used as a parity bit. The M bit, with mask 0x10, determines whether eight or nine bits total are transmitted with each byte, regardless of whether or not the most-significant bit is a parity bit.

The PT bit, with mask 0x01, determines whether even parity or odd parity is used if parity bit generation is enabled. In fact, the program works the same as it did before, but now it is using the secondary serial port instead of the primary port - and you didn’t even have to recompile the code! Although the devices would share the same network, communications would only be understandable by members of the same group. Serial 2 is implemented by a software UART in the controller’s QED-Forth Kernel that uses two of the processor’s PortA I/O pins to generate a serial communications channel. The Serial 2 port is dedicated to RS232 communications at up to 4800 baud. You can operate the port at any baud rate up to 4800 baud; just specify the rate you want before the BAUD2 command. The DECIMAL command makes sure that numbers are interpreted in the decimal base.