이름 : Christian Zavala
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This means that in a master/slave configuration, a master can talk to multiple slaves, all of the slaves can talk back to the master, and every device on the network can hear every other device. When two pair of wires are used for full-duplex communications, one pair is used for the interface generator (driver) to talk to the other device(s) on the RS-422 network, and the second pair is the interface receiver used to listen to an other device (not devices, since only one driver can be on this pair of wires) on the network. But, the RS-232 standard allows for synchronous communications, which is not compatible with the IBM PC serial port, as well as asynchronous communications, which can be. Again, this protocol is not part of the RS-232 standard, even though many engineers think of this protocol as "RS-232". This was done since this protocol is a very common bit format used with serial communications. Since the driver and receiver are differential circuits, the input and output voltages are specified as differential, but these voltages are also referenced to a circuit common.

The driver must not exceed 10V differential, or 6V common mode (outputs relative to circuit common). This is a rather convoluted way of saying pin 7 of the DB-25 connector is used as a signal common. The RS-232 standard does not include a line length limit, but practical limits of the electrical signal levels prevent long lengths. But, since existing RS-232 compatible peripherals still functioned with it, it was still regularly called an "RS-232 port". 12V and -7V. If the desktop's port is ESD protected damage may not occur, but there is no guarantee. 12V and -12V as their voltage sources. Because a mark (logic 1) condition is traditionally represented (e.g. in RS-232) with a negative voltage and space (logic 0) represented with a positive one, A may be considered the non-inverting signal and B as inverting. The UART connected to the RS-232 driver/receiver controls the protocol of the bits being transferred. Please note that a RS-485 network is a single pair of wires, but there is nothing in the RS-485 standard that prevents more than one RS-485 network from being used by each device.

This standard is for a network of a single balanced pair of wires. RS-422 includes the voltage levels of the two wires when a binary 0 or 1 is on the RS-422 lines, but specifically excludes the logic function of the generator or receiver. Other standards such as EIA-530 reference RS-422 for electrical signal levels, and include multiple signals on multiple pairs of wires. In summary, the EIA/TIA standards (which are commonly miscalled RS standards) are the physical layer which include electrical signal levels and RS-232 includes the connector. The RS-232 standard defines a DB-25 and a 26-pin alternate connector, the function of each of the pins in the connector (called circuits), and the electrical characteristics of the signals that are on the "circuits". The ground signal is a common return for all signals. EIA-530 signals include transmit. The 9-pin "RS-232" connector used for the IBM PC-AT serial port is not specified in RS-232. The connector resides in layer one of the OSI model and RS-232 includes the connector. Alas, a long 3-conductor cable intended for RS-232 can not be switched to full-duplex RS-485, which requires 5 conductors. But, the RS-232 connection from the computer to the modem would still be full-duplex.

The RS-232 standard includes secondary serial data circuits (secondary TX data, and secondary RX data), three clocks (timing elements) for synchronous serial data transfer, Signal Quality Detector, and more. When IBM changed to the new connector they also changed the electrical signal levels. The serial port used a D-sub, B-shell, 25-pin connector (commonly called a DB-25) and RS-232 electrical signal levels, which made it "RS-232 compatible" or compatible with the RS-232 standard. Half-duplex RS-232 implementations exist but require all of the hardware and wires that a full-duplex network requires. EIA-485 specifies bidirectional, half-duplex data transmission. These old and slow microprocessors did not always have the horsepower to monitor the timing of both the incoming and outgoing bits, limiting the system to half-duplex. The term network is used to define the wires, terminations, bias networks, and all devices connected as a whole system. The system will operate on 85-265 Vac 50-60 Hz which covers the world standard voltages. Voltages of less than 200mV are undefined. Receiver(s) inputs at a minimum of 200mV differential. There are 2 inputs for limit switch inputs, and 2 inputs for encoder phase inputs. The graph at right, which is often shown in these app-notes, shows a limit of 1200 meters/DC at one end and 14 meters/10 Mbit at the other.

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