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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). If you do this now, remember to move the QScreen Controller’s serial connector back to Serial Port 1, and to change the terminal’s baud rate back to 19200 baud using the "Comm" item under the terminal’s "Settings" menu. You can operate the port at any baud rate up to 4800 baud; just specify the rate you want before the BAUD2 command. Typing a carriage return at the terminal should now produce the familiar "ok" response via the Serial2 port. 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. Also, several non-serial interrupts can stack up; if they have higher priority than the serial interrupts, they will be serviced before the Serial2 interrupt routine, and again a serial input or output bit may be lost. Routines that temporarily disable interrupts for significant periods of time can also interfere with the Serial2 port. The primary serial port, Serial1, is supported by the 68HC11's on-chip hardware UART (sometimes called a USART), and does not require interrupts to work properly.

The Control-C Glossary contains a list of functions that temporarily disable interrupts, and the glossary entries give further information regarding how long interrupts are disabled. Alarm systems: Rs485 cables in alarm systems help transfer alarm signals and information from alarm devices to the control center. The QED-Forth kernel includes pre-coded drivers that configure and control the SPI for maximum speed data transfers. This chapter describes those drivers, and presents code that makes it easy to configure the SPI for different data transfer rates and formats. Data rates of 100Kbps can be achieved over distances of up to 1200 meters. The branches must be no longer than 1200 m! It is important to note that when the CPHA bit is 0, the /SS line must be de-asserted and re-asserted between each successive data byte exchange (68HC11 Reference Manual, Section 8.3.2). If the CPHA bit is 1, the /SS line may be tied low between successive transfers. The data exchange format may be a line of ascii text. If more than one slave tried to drive the transmit line simultaneously, their serial drivers would fight with each other for control of the bus. To ensure that no two devices drive the network at the same time, it is necessary that each slave device be able to disable it’s own RS-485 data transmitter.

After configuring the SPI system to communicate on a properly connected network of devices, sending and receiving data is as simple as writing and reading a register. The SPI can transfer data much more rapidly than an asynchronous serial link - its maximum rate is 2 Megabits/second. The maximum sustainable baud rate on the secondary serial port is 4800 baud. Both the local and remote UARTs must be configured for the same baud rate. To avoid contention on the RS485 bus, the application software must assure that only one transmitter is enabled at a time. In half-duplex mode, rs485 cable you can only transmit or receive data at any given time. TXSoil can transmit the humidity to a Web server or to a VisualVision's display / concentrator such as DisplayRX or ControlHUB or RXTXeasy GSM - with adjustable interval, remaining for the rest of the time in standby with very low consumption. If you are running Serial2 at 4800 baud, the rest of your application must be able to function properly using the remaining portion of the CPU time. The Serial2 channel is always configured for RS232 communications, and can sustain baud rates up to 4800 baud.

Although the maximum standard baud rate of the primary serial port is 19200 baud, nonstandard baud rates of over 80 Kbaud can be attained by the 68HC11's on-chip UART and the onboard RS232 driver. The maximum Serial2 communications rate is 4800 baud. Moreover, if Serial2 is running full duplex at 4800 baud, any other interrupt service routine that takes longer than 100 µs is likely to cause a problem. Pin 3 of PortA is the Serial2 input, and pin 4 of PortA is the Serial2 output. 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. The SCK (serial clock) pin is a configurable synchronous data clock output. The UART Wildcard provides two simultaneous communications links, each configurable as RS232, RS485 or RS422. To interface devices that support synchronized serial interfaces, but are not configurable like the QScreen, determine the device’s requirements for clock phase and polarity and configure the QScreen’s CPHA and CPOL accordingly. RS-485, like RS-422, can be made full-duplex by using four wires.