Serial, RS232: Difference between revisions

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==Pinouts==
<TR><TD>Pin No.</TD><TD>Name</TD><TD>Dir</TD><TD>Notes/Description</TD></TR>
<TR><TD>1</TD><TD>DCD</TD><TD>IN</TD><TD>Data Carrier Detect. Raised by DCE when modem synchronized.</TD></TR>
<TR><TD>2</TD><TD>RD</TD><TD>IN</TD><TD>Receive Data (a.k.a RxD, Rx). Arriving data from DCE.</TD>
</TR>
<TR><TD>3</TD><TD>TD</TD><TD>OUT</TD><TD>Transmit Data (a.k.a TxD, Tx). Sending data from DTE.</TD></TR>
<TR><TD>4</TD><TD>DTR</TD><TD>OUT</TD><TD>Data Terminal Ready. Raised by DTE when powered on. In auto-answer mode raised only when RI arrives from DCE.</TD></TR>
<TR><TD>5</TD><TD>SGND</TD><TD>-</TD><TD>Ground</TD></TR>
<TR><TD>6</TD><TD>DSR</TD><TD>IN</TD><TD>Data Set Ready. Raised by DCE to indicate ready.</TD></TR>
<TR><TD>7</TD><TD>RTS</TD><TD>OUT</TD><TD>Request To Send. Raised by DTE when it wishes to send. Expects CTS from DCE.</TD></TR>
<TR><TD>8</TD><TD>CTS</TD><TD>IN</TD><TD>Clear To Send. Raised by DCE in response to RTS from DTE.</TD></TR>
<TR><TD>9</TD><TD>RI IN Ring Indicator. Set when incoming ring detected - used for auto-answer application. DTE raised DTR to answer.</TD></TR>


== Achievable distances==
== Achievable distances==

Revision as of 20:12, 17 March 2009

Overview

Communication as defined in the RS232 standard is an asynchronous serial communication method. The word serial means, that the information is sent one bit at a time. Asynchronous tells us that the information is not sent in predefined time slots. Data transfer can start at any given time and it is the task of the receiver to detect when a message starts and ends.



Voltages

The signal level of the RS232 signal can have two states. A high bit, or mark state is identified by a negative voltage and a low bit or space state uses a positive value. This might be a bit confusing, because in normal circumstances, high logical values are defined by high voltages also. The voltage limitations are shown below.

RS232 voltage values
LevelTransmitter
capable (V)
Receiver
capable (V)
Space state (0)+5 ... +15+3 ... +25
Mark state (1)-5 ... -15-3 ... -25
Undefined--3 ... +3

Pinouts

Pin No.NameDirNotes/Description 1DCDINData Carrier Detect. Raised by DCE when modem synchronized. 2RDINReceive Data (a.k.a RxD, Rx). Arriving data from DCE. 3TDOUTTransmit Data (a.k.a TxD, Tx). Sending data from DTE. 4DTROUTData Terminal Ready. Raised by DTE when powered on. In auto-answer mode raised only when RI arrives from DCE. 5SGND-Ground 6DSRINData Set Ready. Raised by DCE to indicate ready. 7RTSOUTRequest To Send. Raised by DTE when it wishes to send. Expects CTS from DCE. 8CTSINClear To Send. Raised by DCE in response to RTS from DTE. 9RI IN Ring Indicator. Set when incoming ring detected - used for auto-answer application. DTE raised DTR to answer.

Achievable distances

The maximum distance that RS323 can go varies depending on Bit Rate and also the capacitance of the wire itself. Texas Instruments states that RS 232 maximum cable length is 50 feet, or the cable length equal to a capacitance of 2500 pF. Depending on the cable such as Category 5 Twisted pair the maximum achievable distance at 19200 is 157 feet.

here is a quick chart showing theoretical limits as various data rates for RS232 cable length according to Texas Instruments

Baud rateMaximum cable length (ft)
1920050
9600500
48001000
24003000

External Links