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. Even parity means that the bits sum to an even number, and odd parity means that the bits sum to an odd number. Even RS485 is not commonly as popular as RS232 it is extremely useful for converters in industrial and commercial environments. In this sketch, the slave ARIES (ARIES v2) receives the command from the master (ARIES v3) through the MAX485 module by using the RS485 protocol. It receives signals on one network and re-transmits them on another. However since only a true RS485 network can have addressable serial RS485 devices, the RS232 converter needs to be addressable either by software or by DIP switches when using it in this type of configuration. The QScreen Controller has two serial communications ports: a primary serial port called Serial 1 that supports both RS232 and RS485 protocols, and a secondary serial port called Serial 2 that supports RS232. The Serial 1 port is implemented with the 68HC11's on-chip hardware UART (Universal Asynchronous Receiver/Transmitter). 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.

RS485 is another protocol supported by the primary serial port on the QScreen Controller. Newer protocols include the full duplex RS422 and the half duplex RS485 protocols, each of which drives differential 0 to 5 volt signals on the serial cable. RS485 uses the same differential signaling scheme as RS422, and hence has the same superior signal-to-noise characteristics and range described above. Done that establishes the RS485 receive mode is coded such that it waits until all queued (pending) characters have been transmitted before the driver chip is taken out of transmit mode. The RS422 driver and receiver use separate differential conductor pairs on the serial cables, enabling full duplex communications. Each RS422 driver transmits a differential pair of output signals at 0 and 5 volts. Characters may be lost if the transmit driver is turned off while pending characters are still being transmitted. Each RS232 driver uses inverting logic and implements a single-ended bipolar output voltage (that is, one signal that swings above and below ground). The UART Wildcard supports any baud rate produced by the above formula. The RS422 receiver converts the differential signal to the 0 to 5 volt logic signal required by the UART circuitry. A RS232 - RS422 converter is a 4-wire, full-duplex, rs485 cable differential protocol with multi-drop capabilities and a recommended distance limit of 4000ft. ANSI/TIA/EIA-422-B is the American national standard for the RS422 protocol.

Because differential signals have inherently better signal-to-noise properties, reliable RS422 communications can be sent over much longer distances compared to RS232. 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 has a special capacitive sensor designed by us, efficient and of good precision, waterproof, resistant to oxidation and not subject to variations due to salinity and soil composition: better than this there are only the "extraction pressure" sensors (which we do not propose because they are not durable and also the sensor alone costs hundreds of euros). There is also the GSM version; especially useful when only one sensor is needed in a remote location where other types of transmission cannot be used. The master is in charge of designating which receiver is on at any one time. Similarly, when establishing the transmit mode, the application software is responsible for ensuring that the RS485 receiver is not disabled until all expected characters have been received.

In this tutorial, we will discuss how to communicate between two ARIES boards with the help of the RS485 (Modbus RTU) serial data communication protocol. Handles all serial data on a bit by bit basis. An optional parity bit can be specified to enable error detection by the UART. When this bit is high, the transceiver is in transmit mode. After the slave transmission is complete, the slave puts itself back into receive mode so that the master can transmit additional commands. In this manner, data can be exchanged between the master and each slave on the bus. The master can instruct a single slave to go into transmit mode, and then the master can put itself into receive mode, thereby allowing the master to retrieve data from the slave. A single analog input meter or transmitter can stream readings to a PC at up to 60 readings per second and the Custom ASCII protocol set to continuous (or streaming) model. If on the other hand each terminal can accept only a single cable, a proper branch must be created using three auxiliary terminals for each instrument to be connected.