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예식일 : 10 Questions and Answers to RS485 Standard
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Normally required once the system has reached it's quiescent state, when no drivers are driving the bus. Pull-up/Pull-down resistors (Idle-line failsafe) at one end of the 485 bus may be used to bring the line voltage to a steady state (200mV) value at the end of a transmission; when all drivers are in the passive state. Up to 32 transmitters and 32 receivers may be interconnected in any combination, including one driver and multiple receivers (multi-drop), or one receiver and multiple drivers. Common standards: RS232 RS422 RS449 RS485 20 mA current loop Serial data transmission standards including RS232, RS422, RS423, and RS485 were widely used for many data links, proving effective connectivity for the day. R1202 sets the peak current (Ipeak) used to actuate the solenoid. The number of loads, the termination resistance 60 ohms (120 ohms per side), and the required (turn-on) current of the receivers. Rbias- are 1440Ω and Rterm is 120Ω there will be 0.2V of bias across the termination resistor.

Faster rise times will result in greater ringing amplitude. A higher value termination resistor will reduce the DC losses associated with extreme line lengths, allowing for much longer line lengths at the cost of ringing on the wires. The value of each termination resistor should be equal to the cable characteristic impedance (typically, 120 ohms for twisted pairs). EIA-485 requires a 120 Ohm line impedance (normally Shielded Twisted pair 'STP'), 120W (10%, 1/2 watt) terminations at both ends of the line (at the Receivers). EIA-485 specifies bidirectional, half-duplex data transmission. RS422 This standard gives a much higher data rate than RS232, but it uses differential transmission techniques. Many RS422 devices are compatible with RS232. Read more about RS422. Typically Telecom applications are more I/O intensive than standard controllers. I/O Expansion Modules are provided modular approach to extending the functionality of EMS controllers in specific applications. It is very handy for anything that has an Ethernet port for the ModbusTCP, including devices like Raspberry Pi based controllers industrial controllers. A number of specifications use EIA-485 as the electrical standard, including SCSI-2, SCSI-3, BitBus, and Profibus. The RS-485 hardware generally receives on the receiver every byte that was transmitted by every device on the shared medium, including the local transmitter.

Section 4 defines the electrical characteristics of the generator (transmitter or driver), receiver, transceiver, and system. If both the driver and receiver of the devices on the network have no inversion, (or If both the driver and receiver of the devices are inverted) then the A and B lines of the devices should be connected together. This was developed in 1962 when the need for forms of transmitting data from modems attached telephone lines to remote communications equipments became apparent. Serial data communications standards - RS-232, RS-422, & RS-485 were widely used for data transfer providing easy connectivity for the time and they can still be found today. With RS232 well established and the need for faster communications and over longer distances, further standards beyond RS232 were introduced. However the other standards that have been introduced more recently provide higher levels of performance that are very useful in may applications. RS232 (single-ended) was introduced in 1962, and despite rumors for its early demise, has remained widely used through the industry. RS232 RS-232 is the most widely used serial standard that is in use. RS-232 defines thirteen "standard" interface types lettered A through M. None of these match IBM's implementation of its serial port.

Once RS-232 was established an equivalent standard was written for the ITU (International Telecommunications Union) to provide a more international standard. The EIA is the Electrical Industries Association and the TIA is the Telecommunications Industries Association. The 'RS' stands for Recommended Standard, although later these standards were formally adopted by the EIA / TIA in the USA. Although a number of standards were introduced, RS485 standard the most widely used are RS-422 and RS485. A number of devices are being produced which represent 1/4 or 1/8 the unit load. This allows a complete turnkey system to be implemented within the unit. This allows RS-485 to transmit over longer distances than RS-232. RS485 RS-485 is a standard that allows high speed data transmission along with multiple transmitters and receivers and this makes it able to be incorporated as a network solution. No maximum bus length is given for RS485, but ends up around 1200 meters at 200kbps or 50 meters at 10Mbps. The speed of the system and distance between devices is determined in large amount by the inter-connecting cable.