For those of you interested in the details, here’s how it works: The low-level serial driver routines named Key(), AskKey() and Emit() are revectorable routines that can be redirected to use either of the serial ports. 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. What made it such an advancement over RS232 was the fact that it could transmit not only a single device to device transmission, but also a communications bus to connect multiple devices at once. Another advantage over RS232 that I mentioned earlier is the number of connectable devices. RS423 is another single ended specification with enhanced operation over RS232; however, it has not been widely used in the industry. 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).

The basic rate is 54 Mb / s, but in practice works best in the range of 20 Mb / sRadio network in the case of district heating has proven to be an excellent alternative to other types of communication systems and in this application is an innovative solution. 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. A true multi-point network consists of multiple drivers and receivers connected on a single bus, where any node can transmit or receive data. RS485 meets the requirements for a truly multi-point communications network, and the standard specifies up to 32 drivers and 32 receivers on a single (2-wire) bus. The connection between two or more elements (drivers and receivers) should be considered a transmission line if the rise and/or fall time is less than half the time for the signal to travel from the transmitter to the receiver.

Electronic data communications between elements will generally fall into two broad categories: single-ended and differential. RS422 (differential) was designed for greater distances and higher Baud rates than RS232. RS232 has numerous handshaking lines (primarily used with modems), and also specifies a communications protocol. In general if you are not connected to a modem the handshaking lines can present a lot of problems if not disabled in software or accounted for in the hardware (loop-back or pulled-up). 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. If there is a large potential difference between neutral and earth, this could negatively affect the measurement, in the case of instruments with non-galvanically isolated measurement inputs. If you're sitting in the office right now, and you look to see your thermostat, there's usually RS-485 transceivers connecting that from there to basically the control unit in the building.

The rubber buttons offer limited liquid resistance while the wall mount unit can be for indoor use as the 720 SM, shown below or, mounted in a weather resistant enclosure - 720 SMO. The master initiates a communications request to a "slave node" by addressing that unit. 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. 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). 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. Also, RS485 drivers are able to withstand "data collisions" (bus contention) problems and bus fault conditions. RS485 extends the common mode range for both drivers and receivers in the "tri-state" mode and with power off. Differential signals can help nullify the effects of ground shifts and induced noise signals that can appear as common mode voltages on a network.

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