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We tried to build an organic system so that whoever gets a TXtemp, TXsoil sensor or a bridge for RS232 or ModBus sensors and devices like TXdata can immediately use them without wasting time in configurations (and we also took the opportunity to insert some things into our system some "extra" not foreseen by the standards!). It is interesting to measure the humidity of the ground, but we have also thought about other things; and then we have TXtemp to measure the temperature (one of the uses of TXtemp is in association with SuperClock), and for practically any type of measurement we have TXdata (RS232, RS485 ModBus) - which can be connected to thousands of existing third-party professional RS232 or ModBus meters (and there is something for all needs: temperature and humidity meters, anemometers, voltage meters, energy, light meters, water meters, presence sensors, brightness sensors, soil humidity sensors, etc. ; practically all professional meters are available in ModBus or RS232 standard; and not just meters). Each of the two channels on the UART Wildcard can be configured for RS232, RS422, or RS485. The UART Wildcard provides two simultaneous communications links, each configurable as RS232, RS485 or RS422.

A modem (modulator/demodulator) provides a way of encoding digital data as a set of audio signals that can be sent over a telephone line. The normal way to implement this is with a two wire system with differential signal levels. Each RS232 driver uses inverting logic and implements a single-ended bipolar output voltage (that is, one signal that swings above and below ground). High (mark) parity means that the parity bit is always logic 1 at the UART, and low (space) parity means that the parity bit is always logic 0 at the UART. At the UART, a logic high (5 volts) is called a mark, and a logic low (0 volts) is called a space. 12 volts and outputs logic level (0 or 5 volt) signals to the UART circuitry. A break sequence forces the serial output to a logic low (space) at the UART. These factors are discussed in more detail in The UART Wildcard: Modem Handshaking Signals. Modem to modem lines often use 1200, 4800, 9600, 14400, 28800, 33600, and 56000 baud. Port to modem communications usually use 300, 1200, 2400, 4800, 9600, 19200, 38400, 57600 and 115200 baud.

The words port and channel are used interchangeably to refer to a serial communications link. By polling the Port A pin or by setting up an interrupt service routine, you can configure the QScreen to ignore the SCK input when /SS is high and keep MISO in a high-impedance state so that it does not interfere with the SPI bus. In the most common multi-drop RS485 protocol, one computer is designated as a master and the rest of the computers or devices on the serial bus are designated as slaves. The master and slave could even exchange ascii QED-Forth commands. The master and slave could even exchange ascii QED-Forth operating system commands. A single master can broadcast commands to all the slaves, and can direct commands to an individual slave using its unique address. If you are using the QScreen as a master device, each external SPI device will require a separate select line (/SS).

Most modems communicate using RS232 and a set of hardware handshaking signals used to regulate data flow. Owing to hardware constraints, if modem handshaking is needed on UART channel 1, then channel 1 must be configured for RS232, and channel 2 cannot be configured for RS232 communications. HP is a company that makes and market particular hardware / software for speciallist application. The Silence() routine searches the incoming serial characters for a pre-determined keyword (for example, the ascii name of this particular slave). When the keyword name is received by the Silence() routine running in the slave, the slave PDQ Board executes RS485Transmit() to send an acknowledgment to the master (which should now be listening to the serial bus to accept the acknowledgment). The only difference between the master and slave devices is that the master initiates the transmission. RS485Receive() to wait for any pending character transmission to complete, then disable the transmitter, and then execute a routine such as Key() to listen to the communications on the serial bus. Each of the two UARTs on the wildcard is capable of full-duplex communications, meaning that both transmission and reception can occur simultaneously (although the RS485 protocol is half duplex as explained below).

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