Introduction to RS-232
interface
RS-232 is standard for
serial data transmission. RS-232 was first introduced in 1960 by the Electronic
Industries Association (EIA) as a Recommended Standard. In the United States, a
standard interconnection between business machine and modem is supplied by the
RS-232 interface. An RS-232 serial port was once a standard feature of a
personal computer, used for connections to modems, printers, mic, data
storage, uninterruptible power supplies, and other peripheral devices.
RS-232 defines the connection
of the sending Data Terminal Equipment (DTE) and Data Communication Equipment (DCE)
to the receiving DCE and DTE.
DTE is a device that forms
part of information processing of a system. Usually, the DTE device is the
terminal (or computer), printer and terminal.
DCE is device that provides
an interface between DTE and communication link. DCE is usually a modem.
Information is sent from
DTE and this information reaches to data link layer. Data link layer converts
the information to 0s and 1s and tells the physical layer to exchange bits with
other physical layer. The sending physical layer converts bit stream to
disturbances and determine the speed of disturbances. These disturbances are
actually voltage. Then, the receiving physical layer detects the disturbances
and converts these disturbances back to bit stream and passes it up to the data
link layer. The data link layer determines that bit stream have no errors, and after
confirmation it passes it up to OSI layer.
RS-232 voltage
specification
Transmitting signal
voltage level
Binary 0 : +5 to +15 Vdc
Binary 1 : -5 to -15 Vdc
Receiving signal voltage
level
Binary 0 : +3 to +13 Vdc
Binary 1 : -3 to -13 Vdc
RS-232 cabling options
RS-232 is available with
either 4, 9 or 25 pins wiring. The 25 pin cable connects every pin, the 9 pin
cable don’t include many of uncommonly pins, the 4 pin cable provide minimum
connections and also provides handshaking ability.
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