Single Ended Versus Differential Data Transmission; Rs-232 Interface; Rs-422 Interface; Rs-485 Interface - Hitachi Abb Rvt Installation Und Betriebsanleitung

3.2. SINGLE ENDED versus DIFFERENTIAL data transmission

Single-ended transmission is performed on one signal line, and the logical state is interpreted with respect to ground.
The main disadvantage of the single-ended solution is its poor noise immunity.
For differential transmission, a pair of signal lines is necessary for each channel. On one line, a true signal is transmit-
ted, while on the second one, the inverted signal is transmitted. The receiver detects voltage difference between the
inputs and switches the output depending on which input line is more positive. Differential data transmission schemes
are less susceptible to common-mode noise than single-ended schemes.

3.3. RS-232 interface

An RS-232 interface is rated for distances up to 15 meters (50 feet). At least three wires are required for an RS-232
interface. Wires are required for Transmit, Receive and Signal Ground. Some devices support additional wires for
communication handshaking. RS-232 hardware is a full-duplex configuration, having separate Transmit and Receive
lines.
Each signal that transmits in an RS-232 data transmission system appears on the interface connector as a voltage
with reference to a signal ground. The RS-232 receiver typically operates within the voltage range of +3 to +12 and -3
to -12 volts.

3.4. RS-422 interface

An RS-422 interface requires at least four wires. Two wires each are used for Transmit and Receive. A fifth wire is
usually required for Signal Ground, when connecting non-isolated devices together. Handshaking lines may also be
supported by some hardware. This interface is full duplex, allowing use of the same software drivers as for RS-232.
The differential drivers allow for distances up to 1200 meters (4000 feet). The receivers of an RS-422 device are al-
ways enabled.

3.5. RS-485 interface

For multi-drop operation, drivers must be capable of tri-state operation.
An RS-485 interface requires at least two wires. In a two-wire configuration, the same pair of wires is used for Trans-
mit and Receive. The two-wire configuration utilizes half-duplex communications. Transmit driver circuits are always
taken off-line or tri-stated, when not in use. This tri-state feature reduces the load on the network, allowing more de-
vices, without the need of special hardware. This interface also uses differential drivers, supporting distances up to
1200 meters (4000 feet).
STATUS
Approved
SECURITY LEVEL
Public
DOCUMENT ID
9AKK107045A9895
RS 48 5 A DAPTE R
REV. LANG. PAGE
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