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To solve the "data collision" problem often present in multi-drop networks hardware units (converters, repeaters, micro-processor controls) can be constructed to remain in a receive mode until they are ready to transmit data. Systems of this type (4-wire, half-duplex) are often constructed to avoid "data collision" (bus contention) problems on a multi-drop network (more about solving this problem on a two-wire network in a moment). While a multi-drop "type" application has many desirable advantages, RS422 devices cannot be used to construct a truly multi-point network. There are different sets of standard baud rates in use depending on the application. If your application requires RS485, you can use the secondary serial port (serial2) to program and debug your application code using the RS232 protocol, and use the primary serial port (Serial1) for RS485 communications. Most computers conform to IBM PC AT-compatible RS232 interfaces which use 9-pin D-Type connectors, consequently the PDQ Board brings out its serial ports to two female 9-pin D-Type connectors on the Docking Panel. Two asynchronous communications ports named Serial1 and Serial2 can each be configured for RS232 or RS485 protocols. RS485 extends the common mode range for both drivers and receivers in the "tri-state" mode and with power off.

Note that the local and the remote must share a common ground, so a minimum of 5 wires are required for full duplex RS422 communications: two transmit wires, two receive wires, and a common ground. This helps to minimize the impact of electromagnetic interference, causing the voltage between the two wires to deviate. The RS232 signals are represented by voltage levels with respect to a system common (power / logic ground). The "idle" state (MARK) has the signal level negative with respect to common, and the "active" state (SPACE) has the signal level positive with respect to common. Differential signals can help nullify the effects of ground shifts and induced noise signals that can appear as common mode voltages on a network. For example you need to consider the noise level in the environment surrounding the serial converter. The following table summarizes the available serial channels. Independent channels are established for two-way (full-duplex) communications.

It is NOT necessary to introduce long delays in a network to avoid "data collisions." Because delays are NOT required, networks can be constructed, that will utilize the data communications bandwidth with up to 100% through put. Electronic data communications between elements will generally fall into two broad categories: single-ended and differential. Any number of characters can be sent, and the transmitter will automatically re-trigger with each new character (or in many cases a "bit-oriented" timing scheme is used in conjunction with network biasing for fully automatic operation, including any Baud rate and/or any communications specification, eg. With the introduction of "automatic" repeaters and high-impedance drivers / receivers this "limitation" can be extended to hundreds (or even thousands) of nodes on a network. 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).

RS422 devices. These networks are often used in a half-duplex mode, where a single master in a system sends a command to one of several "slave" devices on a network. RS422. RS422 is also specified for multi-drop (party-line) applications where only one driver is connected to, and transmits on, a "bus" of up to 10 receivers. Differential data transmission (balanced differential signal) offers superior performance in most applications. RTS (Request to send) does have some utility in certain applications. The master initiates a communications request to a "slave node" by addressing that unit. Typically one device (node) is addressed by the host computer and a response is received from that device. The specification allows for data transmission from one transmitter to one receiver at relatively slow data rates (up to 20K bits/second) and short distances (up to 50Ft. @ the maximum data rate). When communicating at high data rates, or over long distances in real world environments, single-ended methods are often inadequate. 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.

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