01-09-2012, 05:02 PM
Introduction to Serial Communication
[attachment=33141]
Introduction
The purpose of this application note is to attempt to describe the main elements in Serial
Communication. This application note attempts to cover enough technical details of RS232,
RS422 and RS485.
DCE and DTE Devices
DTE stands for Data Terminal Equipment, and DCE stands for Data Communications
Equipment. These terms are used to indicate the pin-out for the connectors on a device and the
direction of the signals on the pins. Your computer is a DTE device, while most other devices
such as modem and other serial devices are usually DCE devices.
RS-232 has been around as a standard for decades as an electrical interface between
Data Terminal Equipment (DTE) and Data Circuit-Terminating Equipment (DCE) such as
modems or DSUs. It appears under different incarnations such as RS-232C, RS-232D, V.24,
V.28 or V.10. RS-232 is used for asynchronous data transfer as well as synchronous links such
as SDLC, HDLC, Frame Relay and X.25
Synchronous data transfer
In program-to-program communication, synchronous communication requires that each
end of an exchange of communication respond in turn without initiating a new communication. A
typical activity that might use a synchronous protocol would be a transmission of files from one
point to another. As each transmission is received, a response is returned indicating success or
the need to resend.
Asynchronous data transfer
The term asynchronous is usually used to describe communications in which data can be
transmitted intermittently rather than in a steady stream. For example, a telephone conversation
is asynchronous because both parties can talk whenever they like. If the communication were
synchronous, each party would be required to wait a specified interval before speaking.
The difficulty with asynchronous communications is that the receiver must have a way to
distinguish between valid data and noise. In computer communications, this is usually
accomplished through a special start bit and stop bit at the beginning and end of each piece of
data. For this reason, asynchronous communication is sometimes called start-stop transmission.
[attachment=33141]
Introduction
The purpose of this application note is to attempt to describe the main elements in Serial
Communication. This application note attempts to cover enough technical details of RS232,
RS422 and RS485.
DCE and DTE Devices
DTE stands for Data Terminal Equipment, and DCE stands for Data Communications
Equipment. These terms are used to indicate the pin-out for the connectors on a device and the
direction of the signals on the pins. Your computer is a DTE device, while most other devices
such as modem and other serial devices are usually DCE devices.
RS-232 has been around as a standard for decades as an electrical interface between
Data Terminal Equipment (DTE) and Data Circuit-Terminating Equipment (DCE) such as
modems or DSUs. It appears under different incarnations such as RS-232C, RS-232D, V.24,
V.28 or V.10. RS-232 is used for asynchronous data transfer as well as synchronous links such
as SDLC, HDLC, Frame Relay and X.25
Synchronous data transfer
In program-to-program communication, synchronous communication requires that each
end of an exchange of communication respond in turn without initiating a new communication. A
typical activity that might use a synchronous protocol would be a transmission of files from one
point to another. As each transmission is received, a response is returned indicating success or
the need to resend.
Asynchronous data transfer
The term asynchronous is usually used to describe communications in which data can be
transmitted intermittently rather than in a steady stream. For example, a telephone conversation
is asynchronous because both parties can talk whenever they like. If the communication were
synchronous, each party would be required to wait a specified interval before speaking.
The difficulty with asynchronous communications is that the receiver must have a way to
distinguish between valid data and noise. In computer communications, this is usually
accomplished through a special start bit and stop bit at the beginning and end of each piece of
data. For this reason, asynchronous communication is sometimes called start-stop transmission.