For Serial1 RS232 operation: Remove the jumper shunt from "1 485En" (J4). 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 default baud rate for both Serial1 and Serial2 is 115200 baud after a factory cleanup. 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. Now select the "Comm" item in the "Settings" menu of the Terminal program, and click on 1200 baud (or whatever baud rate you selected in the command above). While running this program, the parity settings of Mosaic Terminal may be adjusted, and in each case the message that matches current settings will appear clearly while the other messages will appear garbled.

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. If two bits are received incorrectly, the error will go unnoticed by parity checking. If PT is set, all transmitted bytes with a parity bit will have an odd number of total '1' bits. 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! We’ll use code from the GETSTART.c program which was introduced in the chapter titled Your First Program.

The default serial routines used by the onboard kernel assume that full duplex communications are available, so you cannot use the RS485 protocol to program the controller. If your application requires use of the secondary serial port as well as other interrupt routines, the key is to keep the interrupt service routines short and fast. The PDQ Board's two serial ports support limited use of generating a parity bit. The UART Wildcard provides two simultaneous communications links, each configurable as RS232, RS485 or RS422. The RS232 protocol specifies the use of two separate grounds, a signal ground and a protective (or "chassis") ground. 1. Use 0603 SMT sized resistor packages. That places a 120 Ω resistor across the RS485 differential line at the driver chip. 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. Grounds between buildings may vary by a small voltage, but with very low impedance and hence the possibility of catastrophic currents - enough to melt signal cables, PCB traces, and transceiver devices.

If the /SS pin of the master is an input and if a low input level is detected, the processor sets the MODF bit in the SPI status register a "mode fault" condition. The QED-Forth kernel includes pre-coded drivers that configure and control the SPI for maximum speed data transfers. The SPE bit turns on the SPI system. The diagram below shows potentials of the A (blue) and B (red) pins of an RS-485 line during transmission of one byte (0xD3, least significant bit first) of data using an asynchronous start-stop method. The data bits are also transmitted in reverse order, with the least significant bit transmitted first, after a start bit. The end devices are responsible for terminating the cable so that there are no reflections from the cable ends. 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.

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