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It may be used to control video surveillance systems or to interconnect security control panels and devices such as access control card readers. This avoids timing problems (and software changes) that are difficult to deal with in typical systems. RS485 avoids this issue which also allows for shielding of the cables to prevent noise. In general it is very important not to run communications wires in the same trough or conduit or in parallel with AC power cables. The main reason behind using these Ethernet Cables over normal wires is that they provide much better protection against noise creeping in and distortion of the signal over high distances. Digital communications networks implementing the standard can be used effectively over long distances and in electrically noisy environments. Converters in general can be used to change the electrical characteristice of one communications standard into another, to take advantage of the best properties of the alternate standard selected.

While handshaking is still with us, it is usually best to disable it in software (if possible) and/or "loop-back" the pairs of signals (RTS to CTS, DTR to DSR, etc.) While RS232 was rumored to be on the "way out" with the advent of many of the new communications standards, it is still alive and well today. One transmitter and 10 receivers are allowed on a network, with a distance limit of 3600ft. RS422 was on the market prior to RS485; however, due to loading limitations, one of the best uses of RS422 is probably in point-to-point communications, such as RS232 extension cords. Up to 32-nodes (drivers and receivers) are allowed on one multi-drop, bi-directional network. Pre-coded device drivers configure the SPI for a standard data format, and it is easy to customize a data format and baud rate for your application. A typical RS485 network can operate properly in the presence of reasonable ground differential voltages, withstand driver contentious situations, provide reliable communications in electrically noisy environments (good common mode rejection using twisted pair cable, shielding provides additional protection), and support thirty-two or more (many IC manufacturers have 1/2, 1/4, what is rs485 cable 1/8 unit load devices) drivers and receivers on the line.

First, we will go over the Gen 2 and Gen 3 modules, because they are more common. You can do different combinations, for example if you have different Gen modules on your stack. Ideally, the two ends of the cable will have a termination resistor connected across the two wires and two powered resistors to bias the lines apart when the lines are not being driven. The aforementioned SenseCAP Sensor Hub at its stock has only 4 ports to connect RS485 sensors despite it being able to support up to 32 different RS485 sensors. An "Automatic Converter" (RS232 to RS485) will turn on the RS485 transmitter when data is detected on the RS232 port, and revert back into the receive mode after a character has been sent. By converting from single-ended RS232 to differential RS422 and then, converting back from RS422 to RS232 at the other end of the line, distance and noise immunity can be greatly improved. The QVGA Controller offers a unique addition to full duplex RS232: it can place its RS232 transmitter into a high impedance silent mode under software control. In addition there is no good way to add terminations resistors at the ends of a "star" network.

We have built sophisticated instruments using the QScreen Controller that operate very reliably using multiple interrupts in addition to the software UART. In these distributed processing networks, a variety of machines and instruments work locally, but communicate and share data or resources with one another globally using a single serial link. Data rates of up to 10M bps are supported over short distances (40ft.). At the four-thousand foot distance limit, data rates of up to 100K bps are allowable. While the standard only supports low data rates and short line length (50ft.) it is still widely used and, very useful in many applications. Without termination resistors, signal reflections off the unterminated end of the cable can cause data corruption. While it goes against conventional wisdom, and can potentially cause a problem with circulating currents by grounding a shielded cable at both ends, this method is very effective at keeping induced lightening noise away from the communications lines.