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RS-232 (Recommended Standard 232)    RS485

It is a standard recommended for binary serial data signals connecting between a DTE (Data terminal equipment) and a DCE (Data Circuit-terminating Equipment). It is commonly used in computer serial ports.
It can be defined as following:
Electrical signal characteristics such as voltage levels, signal rates, timing rate of signals, voltage withstand level, short-circuit behavior, maximum capacitance and cable length.
Connectors and pin identification.
Commonly-used signals are:

Transmitted Data (TxD)
Data sent from DTE to DCE.

Received Data (RxD)
Data sent from DCE to DTE.

Request To Send (RTS)
Affirmed by DTE to prepare DCE to receive data. This may require action on the part of the DCE, e.g. transmitting a carrier or reversing the direction

Clear To Send (CTS)
Asserted by DCE to acknowledge RTS and allow DTE to transmit.

Data Terminal Ready (DTR)
Claimed by DTE to indicate that it is ready to be connected.When this signal is de-asserted, the modem can return to its standby mode, immediately hanging up any calls in progress.

Data Set Ready (DSR)
Affirmed by DCE to indicate an active connection. If DCE is not a modem (e.g. a null modem cable or other equipment), this signal should be permanently asserted (set to 0), possibly by a jumper to another signal.

Data Carrier Detect (DCD)
Affirmed by DCE when a connection has been established with remote equipment.

Ring Indicator (RI)
Affirmed by DCE when it detects a ring signal from the telephone line.
Glossary of Abbreviations.
CTS Clear To Send [DCE --> DTE]
DCD Data Carrier Detected (Tone from a modem) [DCE --> DTE]
DCE Data Communications Equipment eg. modem
DSR Data Set Ready [DCE --> DTE]
DSRS Data Signal Rate Selector [DCE --> DTE]
DTE Data Terminal Equipment eg. computer, printer
DTR Data Terminal Ready [DTE --> DCE]
FG Frame Ground
NC No Connection
RCk Receiver (external) Clock input
RI Ring Indicator (ringing tone detected)
RTS Request To Send [DTE --> DCE]
RxD Received Data [DCE --> DTE]
SG Signal Ground
SCTS Secondary Clear To Send [DCE --> DTE]
SDCD Secondary Data Carrier Detected (Tone from a modem)      
[DCE --> DTE]
SRTS Secondary Ready To Send [DTE --> DCE]
SRxD Secondary Received Data [DCE --> DTE]
STxD Secondary Transmitted Data [DTE --> DTE]
TxD Transmitted Data [DTE --> DTE]