Synchronous And Asynchronous Communication - ZyXEL Communications U-1496 series User Manual

telephone network and reach the other modem. The remote modem
translates the analog signal received back into data
(demodulation) and sends the information to the receiving end
computer. Modems are telephones for computers, what
they use to talk to each other.
((*MODE-02*; Modem as used in computer communications))
WHAT ARE DTE AND DCE
DTE and DCE are terminologies used in data communication. DTE stands for Data Terminal
Equipment and DCE stands for Data Circuit terminating Equipment (Data Communication
Equipment). Referring to Fig. 2.1, the computer or terminal is the DTE and the modem is the
DCE.
WHAT IS RS-232C OR EIA-232D
RS-232C is the Recommended Standard (RS) by the Electronic
Industries Association (EIA) defining the serial communication
interface between a DTE and a DCE. The most commonly used
revision is the "C" revision. For "D" revision, it changes the
prefix to EIA. Except for a few added, but not commonly used
signals, there is no practical difference between the "C" and "D"
revisions. RS-232C is equivalent to CCITT V.24 and V.28.
WHAT IS A SERIAL PORT
A serial port is the serial data connector together with its
internal circuit on the DTE or DCE with electrical and mechanical
characteristics according to RS-232C. Since some signals are
going from the DTE port to DCE port, and some signals are going
in the other direction, the signal pin is a transmitter on one
port and a receiver on the other. The DTE serial port is
different from the DCE serial port in terms of signals on the
connector pins. There are also mechanical differences in terms of
male or female connectors.
SERIAL RS-232C CABLE
A serial RS-232C cable is used to connect a DTE port to a DCE
port. A normal RS-232C connector has 25 pins and a normal RS-232C
cable has 25 wires. Many signals in the RS-232C are not used in
common applications and a 9-wire RS-232C cable is sufficient in
most applications. The PC-AT's serial port has only 9 connector
pins, eliminating the unnecessary pins.

SYNCHRONOUS AND ASYNCHRONOUS COMMUNICATION

There are two kinds of serial data communication. One is called
synchronous and the other is called asynchronous. In synchronous
communication, data is transmitted and received bit by bit and is
timed by an accompanying clock signal. In asynchronous
communication, data is sent character by character (or octet by
octet), the idle time between characters is variable. No clock