1184:. These modems disable their transmitters when not required and must transmit a synchronization preamble to the receiver when they are re-enabled. The DTE asserts RTS to indicate a desire to transmit to the DCE, and in response the DCE asserts CTS to grant permission, once synchronization with the DCE at the far end is achieved. Such modems are no longer in common use. There is no corresponding signal that the DTE could use to temporarily halt incoming data from the DCE. Thus RS-232's use of the RTS and CTS signals, per the older versions of the standard, is asymmetric.
591:
consequently, the range between −3 and +3 volts is not a valid RS-232 level. For data transmission lines (TxD, RxD, and their secondary channel equivalents), logic one is represented as a negative voltage and the signal condition is called "mark". Logic zero is signaled with a positive voltage and the signal condition is termed "space". Control signals have the opposite polarity: the asserted or active state is positive voltage and the de-asserted or inactive state is negative voltage. Examples of control lines include request to send (RTS), clear to send (CTS),
1118:
583:
2162:
574:
50:
786:
38:
794:
460:
1204:
TIA-232-E by that time) by defining a new signal, "RTR (Ready to
Receive)", which is CCITT V.24 circuit 133. TIA-232-E and the corresponding international standards were updated to show that circuit 133, when implemented, shares the same pin as RTS (Request to Send), and that when 133 is in use, RTS is assumed by the DCE to be asserted at all times.
667:. Use of a common ground limits RS-232 to applications with relatively short cables. If the two devices are far enough apart or on separate power systems, the local ground connections at either end of the cable will have differing voltages; this difference will reduce the noise margin of the signals. Balanced, differential serial connections such as
284:, and so on, designers implementing an RS-232 compatible interface on their equipment often interpreted the standard idiosyncratically. The resulting common problems were non-standard pin assignment of circuits on connectors, and incorrect or missing control signals. The lack of adherence to the standards produced a thriving industry of
295:, such as modem connections, on many computers (with the computer acting as the DTE). It remained in widespread use into the late 1990s. In personal computer peripherals, it has largely been supplanted by other interface standards, such as USB. RS-232 is still used to connect older designs of peripherals, industrial equipment (such as
1629:(Second Interim Report ed.), Office of Developmental Automation and Control Technology, Institute for Computer Sciences and Technology, National Bureau of Standards, Washington, DC, USA: Manufacturing Technology Division, Air Force Materials Laboratory, Wright-Patterson Air Force Base, Ohio 45433, NBSIR 76-1094
288:, patch boxes, test equipment, books, and other aids for the connection of disparate equipment. A common deviation from the standard was to drive the signals at a reduced voltage. Some manufacturers therefore built transmitters that supplied +5 V and −5 V and labeled them as "RS-232 compatible".
753:" are available to solve gender mismatches between cables and connectors. Connecting devices with different types of connectors requires a cable that connects the corresponding pins according to the table below. Cables with 9 pins on one end and 25 on the other are common. Manufacturers of equipment with
1421:
links. Connection of a current-loop device to a compliant RS-232 port requires a level translator. Current-loop devices can supply voltages in excess of the must-withstand voltage limits of a compliant device. The original IBM PC serial port card implemented a 20 mA current-loop interface, which
1296:
Since the relation between the transmitted bit and TT can be fixed in the DTE design, and since both signals traverse the same cable length, using TT eliminates the issue. TT may be generated by looping ST back with an appropriate phase change to align it with the transmitted data. ST loop back to TT
1253:
capability used for testing. When enabled, signals are echoed back to the sender rather than being sent on to the receiver. If supported, the DTE can signal the local DCE (the one it is connected to) to enter loopback mode by setting Local Loop (LL, pin 18) to ON, or the remote DCE (the one the local
1240:
The DTE or DCE can specify use of a "high" or "low" signaling rate. The rates, as well as which device will select the rate, must be configured in both the DTE and DCE. The prearranged device selects the high rate by setting the Data Signal Rate
Selector (DSRS, pin 23) signal to ON. Sometimes called
1108:
for the other connections, and establishes the "zero" voltage to which voltages on the other pins are referenced. The DB-25 connector includes a second "protective ground" on pin 1; this is connected internally to equipment frame ground, and should not be connected in the cable or connector to signal
560:
transmissions are supported by the standard. In addition to the data circuits, the standard defines a number of control circuits used to manage the connection between the DTE and DCE. Each data or control circuit only operates in one direction, that is, signaling from a DTE to the attached DCE or the
1622:
Evans, Jr., John M.; O'Neill, Joseph T.; Little, John L.; Albus, James S.; Barbera, Anthony J.; Fife, Dennis W.; Fong, Elizabeth N.; Gilsinn, David E.; Holberton, Frances E.; Lucas, Brian G.; Lyon, Gordon E.; Marron, Beatrice A. S.; Neumann, Albercht J.; Vickers, Mabel V.; Walker, Justin C. (October
1203:
A symmetric alternative providing flow control in both directions was developed and marketed in the late 1980s by various equipment manufacturers. It redefined the RTS signal to mean that the DTE is ready to receive data from the DCE. This scheme was eventually codified in version RS-232-E (actually
658:
Because the voltage levels are higher than logic levels typically used by integrated circuits, special intervening driver circuits are required to translate logic levels. These also protect the device's internal circuitry from short circuits or transients that may appear on the RS-232 interface, and
179:
has displaced RS-232 from most of its peripheral interface roles. Thanks to their simplicity and past ubiquity, however, RS-232 interfaces are still used—particularly in industrial CNC machines, networking equipment and scientific instruments where a short-range, point-to-point, low-speed wired data
1505:
publishes standard ITR-R V.24 (formerly CCITT standard V.24), "List of
Definitions for Interchange Circuits between Data Terminal Equipment (DTE) and Data Circuit-Terminating Equipment (DCE)" with circuit definitions compatible to those in EIA RS 232. V.24 does not specify signal levels or timing.
1283:
to synchronize data transmission, especially at higher data rates. Two timing signals are provided by the DCE. Pin 15 is the transmitter clock (TCK), or send timing (ST); the DTE puts the next bit on the transmit data line (pin 2) when this clock transitions from OFF to ON (so it is stable during
1191:
converters. RS-485 is a multiple-access bus on which only one device can transmit at a time, a concept that is not provided for in RS-232. The RS-232 device asserts RTS to tell the converter to take control of the RS-485 bus so that the converter, and thus the RS-232 device, can send data onto the
355:
In revision D of EIA-232, the D-subminiature connector was formally included as part of the standard (it was only referenced in the appendix of RS-232-C). The voltage range was extended to ±25 volts, and the circuit capacitance limit was expressly stated as 2500 pF. Revision E of EIA-232
1143:
is generated when the RI signal changes state. Having support for this hardware interrupt means that a program or operating system can be informed of a change in state of the RI pin, without requiring the software to constantly "poll" the state of the pin. RI does not correspond to another signal
737:
The standard does not define a maximum cable length, but instead defines the maximum capacitance that a compliant drive circuit must tolerate. A widely used rule of thumb indicates that cables more than 15 m (50 ft) long will have too much capacitance, unless special cables are used. By
1527:
but specialized for RS-232's voltage levels, connectors, and, where used, clock signals; it collects, stores, and displays the data and control signals, allowing developers to view them in detail. Some simply display the signals as waveforms; more elaborate versions include the ability to decode
691:
RS-232 devices may be classified as Data
Terminal Equipment (DTE) or Data Circuit-terminating Equipment (DCE); this defines at each device which wires will be sending and receiving each signal. According to the standard, male connectors have DTE pin functions, and female connectors have DCE pin
590:
The RS-232 standard defines the voltage levels that correspond to logical one and logical zero levels for the data transmission and the control signal lines. Valid signals are either in the range of +3 to +15 volts or the range −3 to −15 volts with respect to the "Common Ground" (GND) pin;
1207:
In this scheme, commonly called "RTS/CTS flow control" or "RTS/CTS handshaking" (though the technically correct name would be "RTR/CTS"), the DTE asserts RTS whenever it is ready to receive data from the DCE, and the DCE asserts CTS whenever it is ready to receive data from the DTE. Unlike the
1223:
A minimal "3-wire" RS-232 connection consisting only of transmit data, receive data, and ground, is commonly used when the full facilities of RS-232 are not required. Even a two-wire connection (data and ground) can be used if the data flow is one way (for example, a digital postal scale that
1292:
in a long cable. ST must traverse a cable of unknown length and delay, clock a bit out of the DTE after another unknown delay, and return it to the DCE over the same unknown cable delay. When sending data at high speed, the data bit may not arrive in time for the ON to OFF transition of ST.
1195:
Modern communications environments use full-duplex (both directions simultaneously) modems. In that environment, DTEs have no reason to deassert RTS. However, due to the possibility of changing line quality, delays in processing of data, etc., there is a need for symmetric, bidirectional
699:
26-pin connector up to revision C, and makes it mandatory as of revision D. Most devices only implement a few of the twenty signals specified in the standard, so connectors and cables with fewer pins are sufficient for most connections, more compact, and less expensive. Personal computer
692:
functions. Other devices may have any combination of connector gender and pin definitions. Many terminals were manufactured with female connectors but were sold with a cable with male connectors at each end; the terminal with its cable satisfied the recommendations in the standard.
577:
Diagrammatic oscilloscope trace of voltage levels for an ASCII "K" character (4Bh = 01001011b) with 1 start bit, 8 data bits (least significant bit first), 1 stop bit. This is typical for start-stop communications, but the standard does not dictate a character format or bit
662:
Because both ends of the RS-232 circuit depend on the ground pin being zero volts, problems will occur when connecting machinery and computers where the voltage between the ground pin on one end, and the ground pin on the other is not zero. This may also cause a hazardous
678:
Unused interface signals terminated to the ground will have an undefined logic state. Where it is necessary to permanently set a control signal to a defined state, it must be connected to a voltage source that asserts the logic 1 or logic 0 levels, for example with a
1466:– a system like RS-232 but with better impedance and rise time control. One very significant difference: RS-232 uses a positive voltage to indicate a 0 and a negative voltage to indicate a 1. MIL-STD-188 uses a negative voltage for 0 and a positive voltage for a 1.
490:(EMI) and that maximum cable length defined by standards is much shorter (15 meters for RS-232 versus 3–5 meters for USB, depending on the USB version and use of active cables). RS-232 cable lengths of 2000 meters are possible with appropriate line drivers.
1224:
periodically sends a weight reading, or a GPS receiver that periodically sends position, if no configuration via RS-232 is necessary). When only hardware flow control is required in addition to two-way data, the RTS and CTS lines are added in a 5-wire version.
1147:
On an external modem the status of the Ring
Indicator pin is often coupled to the "AA" (auto answer) light, which flashes if the RI signal has detected a ring. The asserted RI signal follows the ringing pattern closely, which can permit software to detect
1287:
Alternatively, the DTE can provide a clock signal, called transmitter timing (TT, pin 24) for transmitted data. Data is changed when the clock transitions from OFF to ON, and read during the ON to OFF transition. TT can be used to overcome the problem of
749:, or use trial and error to find a cable that works when interconnecting two devices. Connecting a fully standard-compliant DCE device and DTE device would use a cable that connects identical pin numbers in each connector (a so-called "straight cable"). "
306:
The standard has been renamed several times during its history as the sponsoring organization changed its name, and has been variously known as EIA RS-232, EIA 232, and, most recently as TIA 232. The standard continued to be revised and updated by the
1254:
DCE is connected to) to enter loopback mode by setting Remote Loop (RL, pin 21) to ON. The latter tests the communications link, as well as both DCEs. When the DCE is in test mode, it signals the DTE by setting Test
Indicator (TI, pin 25) to ON.
418:
The definitions of the two ends of the link are asymmetric. This makes the assignment of the role of a newly developed device problematic; the designer must decide on either a DTE-like or DCE-like interface and which connector pin assignments to
1514:
When developing or troubleshooting systems using RS-232, close examination of hardware signals can be important to find problems. This can be done using simple devices with LEDs that indicate the logic levels of data and control signals.
485:
for local communications. Advantages compared to RS-232 are that USB is faster, uses lower voltages, and has connectors that are simpler to connect and use. Disadvantages of USB compared to RS-232 are that USB is far less immune to
401:
The large voltage swings and requirement for positive and negative supplies increases power consumption of the interface and complicates power supply design. The voltage swing requirement also limits the upper speed of a compatible
1284:
the ON to OFF transition when the DCE registers the bit). Pin 17 is the receiver clock (RCK), or receive timing (RT); the DTE reads the next bit from the receive data line (pin 3) when this clock transitions from ON to OFF.
241:, or others), the framing of characters (start or stop bits, etc.), transmission order of bits, or error detection protocols. The character format and transmission bit rate are set by the serial port hardware, typically a
650:
circuitry to produce the required voltages from a 3 or 5 volt supply. RS-232 drivers and receivers must be able to withstand indefinite short circuits to the ground or to any voltage level up to ±25 volts. The
175:, RS-232 has lower transmission speed, shorter maximum cable length, larger voltage swing, larger standard connectors, no multipoint capability and limited multidrop capability. In modern personal computers,
396:
Because RS-232 is used beyond the original purpose of interconnecting a terminal with a modem, successor standards have been developed to address the limitations. Issues with the RS-232 standard include:
2131:
ITU-T Recommendation V.24 - Data
Communication over the telephone network - List of definitions for interchange circuits between data terminal equipment (DTE) and data circuit-terminating equipment (DCE)
1257:
A commonly used version of loopback testing does not involve any special capability of either end. A hardware loopback is simply a wire connecting complementary pins together in the same connector (see
757:
connectors usually provide a cable with either a DB-25 or DE-9 connector (or sometimes interchangeable connectors so they can work with multiple devices). Poor-quality cables can cause false signals by
586:
RS-232 data line on the terminals of the receiver side (RxD) probed by an oscilloscope (for an ASCII "K" character (4Bh = 01001011b) with 1 start bit, 8 data bits, 1 stop bit, and no parity bits)
291:
Later personal computers (and other devices) started to make use of the standard so that they could connect to existing equipment. For many years, an RS-232-compatible port was a standard feature for
715:
Presence of a 25-pin D-sub connector does not necessarily indicate an RS-232-C compliant interface. For example, on the original IBM PC, a male D-sub was an RS-232-C DTE port (with a non-standard
1590:
437:
No method is specified for sending power to a device. While a small amount of current can be extracted from the DTR and RTS lines, this is only suitable for low-power devices such as
738:
using low-capacitance cables, communication can be maintained over larger distances up to about 300 m (1,000 ft). For longer distances, other signal standards, such as
2139:
1215:
Equipment using this protocol must be prepared to buffer some extra data, since the remote system may have begun transmitting just before the local system de-asserts RTR.
408:
Multi-drop connection among more than two devices is not defined. While multi-drop "work-arounds" have been devised, they have limitations in speed and compatibility.
1320:
A secondary data channel, identical in capability to the primary channel, can optionally be implemented by the DTE and DCE devices. Pin assignments are as follows:
801:
The following table lists commonly used RS-232 signals (called "circuits" in the specifications) and their pin assignments on the recommended DB-25 connectors (see
356:
introduced a new, smaller, standard D-shell 26-pin "Alt A" connector, and made other changes to improve compatibility with CCITT standards V.24, V.28 and ISO 2110.
1520:
1565:
1417:
uses the absence of 20 mA current for high, and the presence of current in the loop for low; this signaling method is often used for long-distance and
1232:
The EIA-232 standard specifies connections for several features that are not used in most implementations. Their use requires 25-pin connectors and cables.
1139:(RI) is a signal sent from the DCE to the DTE device. It indicates to the terminal device that the phone line is ringing. In many computer serial ports, a
1472:– a high-speed system using RS-422 or RS-423 electrical properties in an EIA-232 pinout configuration, thus combining the best of both; supersedes RS-449
565:
manner, supporting concurrent data flow in both directions. The standard does not define character framing within the data stream or character encoding.
1180:
The
Request to Send (RTS) and Clear to Send (CTS) signals were originally defined for use with half-duplex (one direction at a time) modems such as the
481:
deprecated support for the RS-232 compatible serial port of the original IBM PC design. Today, RS-232 has mostly been replaced in personal computers by
777:
cable may be necessary. Gender changers and null modem cables are not mentioned in the standard, so there is no officially sanctioned design for them.
415:
cables can be used to achieve these connections, but these are not defined by the standard, and some such cables use different connections than others.
1212:. However, "hardware flow control" in the description of the options available on an RS-232-equipped device does not always mean RTS/CTS handshaking.
642:
of 25 volts: signal levels of ±5 V, ±10 V, ±12 V, and ±15 V are all commonly seen depending on the voltages available to the
2114:
528:
is not yet running and therefore no network connection is possible. A computer with an RS-232 serial port can communicate with the serial port of an
1587:
2201:
372:
EIA RS-232-C (August 1969) "Interface
Between Data Terminal Equipment and Data Communication Equipment Employing Serial Binary Data Interchange"
378:
TIA TIA/EIA-232-E (1991) "Interface
Between Data Terminal Equipment and Data Communications Equipment Employing Serial Binary Data Interchange"
1494:
1485:
1475:
1491:
TIA-574 – standardizes the 9-pin D-subminiature connector pinout for use with EIA-232 electrical signalling, as originated on the IBM PC/AT
2165:
1672:
EIA standard RS-232-C: Interface between Data Terminal Equipment and Data Communication Equipment Employing Serial Binary Data Interchange
745:
Since the standard definitions are not always correctly applied, it is often necessary to consult documentation, test connections with a
1454:– a functional and mechanical interface that used RS-422 and RS-423 signals; never caught on like RS-232 and was withdrawn by the EIA
1208:
original use of RTS and CTS with half-duplex modems, these two signals operate independently from one another. This is an example of
249:
to RS-232 compatible signal levels. The standard does not define bit rates for transmission, except that it says it is intended for
317:
TIA-232-F Interface Between Data Terminal Equipment and Data Circuit-Terminating Equipment Employing Serial Binary Data Interchange
128:
TIA-232-F Interface Between Data Terminal Equipment and Data Circuit-Terminating Equipment Employing Serial Binary Data Interchange
2129:
1726:
312:
277:(smart and dumb) began to be used, they were often designed to be interchangeable with teletypewriters, and so supported RS-232.
122:. The standard defines the electrical characteristics and timing of signals, the meaning of signals, and the physical size and
1392:
of near +5 V and 0 V puts the mark level in the undefined area of the standard. Such levels are sometimes used with
2181:
2135:
2026:
1870:
1502:
2053:
2186:
2084:
1624:
1895:
108:
53:
319:, issued in 1997. Changes since Revision C have been in timing and details intended to improve harmonization with the
1978:
1821:
1793:
1675:
557:
315:(TIA). Revision C was issued in a document dated August 1969. Revision D was issued in 1986. The current revision is
308:
262:
189:
1241:
Data Rate Select (DRS), this signal should not be confused with the more commonly used Data Set Ready (DSR, pin 6).
1754:
1388:
Other serial signaling standards may not interoperate with standard-compliant RS-232 ports. For example, using the
553:
509:
equipment are programmable via RS-232. Computer manufacturers have responded to this demand by re-introducing the
1548:. Serial line analyzers are available as standalone units, as software and interface cables for general-purpose
280:
Because the standard did not foresee the requirements of devices such as computers, printers, test instruments,
1414:
1175:
1156:
506:
157:
1837:
405:
Single-ended signaling referred to a common signal ground limits the noise immunity and transmission distance.
2191:
1533:
1301:
494:
296:
487:
114:
30:
This article is about the RS-232, standard. For RS-232 variants, including the common 9-pin connector, see
2102:
144:
A serial port complying with the RS-232 standard was once a standard feature of many types of computers.
493:
In fields such as laboratory automation or surveying, RS-232 devices continue to be used. Some types of
411:
The standard does not address the possibility of connecting a DTE directly to a DTE, or a DCE to a DCE.
1781:
561:
reverse. Because transmit data and receive data are separate circuits, the interface can operate in a
664:
723:. Some personal computers put non-standard voltages or signals on some pins of their serial ports.
498:
719:
interface on reserved pins), but the female D-sub connector on the same PC model was used for the
90:
57:
17:
2196:
1906:
1775:
1437:
1105:
1785:
1209:
1128:
connector that used the Ring Indicator signal to notify the host computer when the connected
797:
Male pinout of a 25-pin serial port (D-subminiature, DB-25) commonly found on 1980s computers
444:
The 25-pin D-sub connector recommended in the standard is large compared to current practice.
423:
659:
provide sufficient current to comply with the slew rate requirements for data transmission.
2110:
2080:
1446:
1297:
lets the DTE use the DCE as the frequency reference, and correct the clock to data timing.
789:
Male pinout of a 9-pin (D-subminiature, DE-9) serial port commonly found on 1990s computers
639:
292:
81:
73:
1865:. Dark, Joy, West, Jill (Tenth ed.). Boston, MA, USA: Cengage Learning. p. 267.
1519:
may be used to allow using another serial port to monitor all traffic on one direction. A
1479:
1117:
8:
1990:
1959:
1268:
1197:
873:
848:
592:
431:
274:
149:
720:
1994:
1497:– similar to TIA/EIA-232-F but with support for higher data rates up to 512 kbit/s
1140:
970:
DTE is ready to receive data from DCE. If in use, RTS is assumed to be always asserted.
802:
709:
533:
521:
230:
77:
65:
2019:
Serial Port Complete: COM Ports, USB Virtual COM Ports, and Ports for Embedded Systems
675:
can tolerate larger ground voltage differences because of the differential signaling.
2049:
2022:
1876:
1866:
1817:
1789:
1750:
1679:
1289:
683:. Some devices provide test voltages on their interface connectors for this purpose.
582:
438:
334:, but equipment built to the current standard will interoperate with older versions.
145:
99:
95:
1982:
1149:
680:
525:
219:
Interface mechanical characteristics, pluggable connectors and pin identification.
2036:
1813:
1594:
1532:
or other common codes and to interpret common protocols used over RS-232 such as
1423:
529:
517:
1935:
1646:
426:
and control lines of the interface are intended for the setup and takedown of a
2071:
1549:
1524:
1129:
770:
750:
696:
300:
270:
1986:
1880:
1460:– a descendant of RS-422 that can be used as a bus in multidrop configurations
2175:
2161:
1771:
1767:
1747:
Practical Industrial Data Networks: Design, Installation, and Troubleshooting
1418:
209:
153:
1910:
1683:
363:
EIA RS-232 (May 1960) "Interface Between Data Terminal Equipment & Data"
1553:
1280:
1163:
746:
732:
716:
573:
285:
281:
138:
1463:
647:
643:
562:
545:
502:
463:
454:
246:
225:
Standard subsets of interface circuits for selected telecom applications.
213:
197:
134:
31:
1403:
1389:
1121:
774:
412:
342:
324:
84:
transmission of data. It formally defines signals connecting between a
49:
1556:, and as programs that run on common personal computers and devices.
1394:
759:
655:, or how fast the signal changes between levels, is also controlled.
652:
478:
430:
communication circuit; in particular, the use of handshake lines for
205:
201:
1697:
1267:
Loopback testing is often performed with a specialized DTE called a
1260:
1250:
1181:
769:
If a given cable will not allow a data connection, especially if a
250:
172:
1718:
1516:
1469:
805:
for other commonly used connectors not defined by the standard).
785:
524:, where no monitor or keyboard is installed, during boot when an
427:
347:
329:
1979:"Re: EIA-232 full duplex RTS/CTS flow control standard proposal"
1621:
1166:, allowing a computer that is suspended to answer a phone call.
1506:
Electrical parameters for signals are specified in ITU-R-V.28.
1457:
1451:
1442:
1433:
1407:
1188:
924:
DCE has detected an incoming ring signal on the telephone line.
739:
712:), is prevalent for personal computers and associated devices.
701:
672:
668:
238:
168:
164:
141:. It is still widely used in industrial communication devices.
123:
37:
513:
connector on their computers or by making adapters available.
459:
1541:
1529:
1125:
817:
793:
705:
510:
472:
338:
320:
234:
119:
42:
1545:
1537:
1309:
1305:
823:
754:
242:
245:, which may also contain circuits to convert the internal
148:
used them for connections not only to modems, but also to
1399:
549:
482:
176:
1159:(UPSs) to signal a power failure state to the computer.
708:
connector. This connector, with a different pinout (see
1480:
eight-position, eight-contact (8P8C) modular connectors
1300:
Synchronous clocking is required for such protocols as
1187:
This scheme is also employed in present-day RS-232 to
1104:
The signals are named from the standpoint of the DTE.
853:
DTE is ready to receive, initiate, or continue a call.
516:
RS-232 ports are also commonly used to communicate to
126:
of connectors. The current version of the standard is
1566:
Comparison of synchronous and asynchronous signalling
222:
Functions of each circuit in the interface connector.
466:
x1 card with one RS-232 port on a nine-pin connector
448:
341:
standards include V.24 (circuit identification) and
273:, and the original DCEs were (usually) modems. When
1583:
1581:
1144:that carries similar information the opposite way.
2038:Interface Circuits for TIA/EIA-232-F: Design Notes
229:The standard does not define such elements as the
1445:– a high-speed system similar to RS-422 but with
1436:– a high-speed system similar to RS-232 but with
1162:Certain personal computers can be configured for
536:) as an alternative to monitoring over Ethernet.
2173:
1578:
1482:(which may be improperly called RJ45 connectors)
1176:Flow control (data) § Hardware flow control
1155:The Ring Indicator signal is used by some older
133:The RS-232 standard had been commonly used with
646:circuit. Many RS-232 driver chips have inbuilt
947:DTE requests the DCE prepare to transmit data.
391:
1698:"RS232 Tutorial on Data Interface and cables"
878:DCE is receiving a carrier from a remote DCE.
352:(signal voltage and timing characteristics).
45:connector as described in the RS-232 standard
2073:Fundamentals of RS–232 Serial Communications
1766:
1745:S. Mackay, E. Wright, D. Reynders, J. Park,
1062:Zero voltage reference for all of the above.
434:is not reliably implemented in many devices.
192:(EIA) standard RS-232-C as of 1969 defines:
1429:Other serial interfaces similar to RS-232:
1410:is required to convert the voltage levels.
1218:
780:
269:. The original DTEs were electromechanical
261:RS-232 was first introduced in 1960 by the
1626:Standards for Computer Aided Manufacturing
1617:
1615:
1613:
1611:
1609:
1607:
196:Electrical signal characteristics such as
1422:was never emulated by other suppliers of
1358:Secondary Request To Send (SRTS or S.RTS)
1342:Secondary Transmitted Data (STD or S.TxD)
993:DCE is ready to accept data from the DTE.
359:Specification document revision history:
1933:
1863:CompTIA A+ Guide to IT technical support
1374:Secondary Carrier Detect (SDCD or S.DCD)
1235:
1116:
792:
784:
762:between data and control lines (such as
581:
572:
458:
183:
48:
36:
2016:
1860:
1727:Telecommunications Industry Association
1604:
1366:Secondary Clear To Send (SCTS or S.CRS)
1227:
742:, are better suited for higher speeds.
313:Telecommunications Industry Association
163:Compared with later interfaces such as
14:
2202:Computer-related introductions in 1960
2174:
1976:
1893:
1350:Secondary Received Data (SRD or S.RxD)
901:DCE is ready to receive and send data.
303:ports, and special purpose equipment.
2166:Serial Programming:RS-232 Connections
2136:International Telecommunication Union
1503:International Telecommunication Union
539:
208:of signals, voltage withstand level,
1802:
1780:(2nd ed.). Cambridge, England:
1509:
1488:– low-voltage version of EIA/TIA-232
1383:
1315:
1169:
2083:. 1998-03-09. Application Note 83.
2021:(2nd ed.). Lakeview Research.
1894:Wilson, Michael R. (January 2000).
1279:Some synchronous devices provide a
1244:
253:lower than 20,000 bits per second.
24:
2010:
1664:
721:parallel "Centronics" printer port
544:In RS-232, user data is sent as a
109:data circuit-terminating equipment
80:originally introduced in 1960 for
54:Data circuit-terminating equipment
25:
2213:
2154:
1676:Electronic Industries Association
1274:
1112:
1106:The ground pin is a common return
638:The standard specifies a maximum
595:(DTR), and data set ready (DSR).
568:
449:Role in modern personal computers
309:Electronic Industries Association
263:Electronic Industries Association
190:Electronic Industries Association
27:Standard for serial communication
2160:
1678:, Engineering Department. 1969.
1097:
599:RS-232 logic and voltage levels
381:TIA TIA/EIA-232-F (October 1997)
160:, and other peripheral devices.
2142:from the original on 2015-08-17
2117:from the original on 2017-03-05
2090:from the original on 2017-03-05
2059:from the original on 2017-03-05
1970:
1952:
1927:
1887:
1854:
1830:
1760:
1739:
1711:
1690:
1639:
1157:uninterruptible power supplies
507:computerized numerical control
495:programmable logic controllers
180:connection is fully adequate.
158:uninterruptible power supplies
13:
1:
1571:
1478:– defines RS-232 pinouts for
1124:Courier external modem had a
1039:Carries data from DCE to DTE.
1016:Carries data from DTE to DCE.
686:
2182:Telecommunications equipment
1977:Leedom, Casey (1990-02-20).
1812:. Redmond, Washington, USA:
1084:Connected to chassis ground.
695:The standard recommends the
488:electromagnetic interference
115:data communication equipment
7:
2187:Computer hardware standards
2052:. September 2002. SLLA037.
1810:PC 97 Hardware Design Guide
1597:Landis + Gyr Tutorial (see
1559:
833:
704:connector with the smaller
700:manufacturers replaced the
392:Limitations of the standard
384:ANSI/TIA-232-F-1997 (R2002)
369:EIA RS-232-B (October 1965)
366:EIA RS-232-A (October 1963)
212:behavior, and maximum load
10:
2218:
1838:"Lengths of serial cables"
1782:Cambridge University Press
1173:
1083:
1080:
1061:
1058:
1038:
1035:
1015:
1012:
992:
989:
969:
966:
946:
943:
923:
920:
900:
897:
877:
872:
852:
847:
730:
452:
256:
29:
1523:is a device similar to a
1089:
1067:
822:
816:
813:
810:
726:
499:variable-frequency drives
1896:"TIA/EIA-422-B Overview"
1249:Many DCE devices have a
1219:3-wire and 5-wire RS-232
781:Data and control signals
1934:Lawrence, Tony (1992).
1719:"TIA Facts at a Glance"
1700:. ARC Electronics. 2010
1647:"Connecting the Beast?"
763:
91:data terminal equipment
58:data terminal equipment
1907:National Semiconductor
1861:Andrews, Jean (2020).
1777:The Art of Electronics
1438:differential signaling
1133:
798:
790:
587:
579:
467:
311:and since 1988 by the
61:
46:
2138:(ITU-T). March 1993.
2046:Mixed-Signal Products
2017:Axelson, Jan (2007).
1903:Application Note 1031
1269:bit error rate tester
1236:Signal rate selection
1210:hardware flow control
1174:Further information:
1120:
796:
788:
585:
576:
475:Hardware Design Guide
462:
387:TIA TIA-232-F (R2012)
293:serial communications
184:Scope of the standard
52:
40:
2192:Networking standards
2111:National Instruments
2081:Dallas Semiconductor
2048:(Technical report).
1521:serial line analyzer
1447:unbalanced signaling
1337:7 (same as primary)
1228:Seldom-used features
640:open-circuit voltage
375:EIA EIA-232-D (1986)
275:electronic terminals
267:Recommended Standard
82:serial communication
74:Recommended Standard
1674:. Washington, USA:
874:Data Carrier Detect
849:Data Terminal Ready
803:Serial port pinouts
710:Serial port pinouts
600:
593:data terminal ready
130:, issued in 1997.
1593:2012-11-29 at the
1419:optically isolated
1141:hardware interrupt
1134:
799:
791:
598:
588:
580:
540:Physical interface
468:
231:character encoding
146:Personal computers
66:telecommunications
62:
47:
2103:"RS232C Standard"
2050:Texas Instruments
2028:978-1-931-44806-2
1872:978-0-357-10829-1
1588:Metering Glossary
1510:Development tools
1406:. A chip such as
1384:Related standards
1381:
1380:
1316:Secondary channel
1290:propagation delay
1170:RTS, CTS, and RTR
1102:
1101:
1092:
1081:Protective Ground
1070:
636:
635:
96:computer terminal
16:(Redirected from
2209:
2164:
2150:
2148:
2147:
2125:
2123:
2122:
2098:
2096:
2095:
2089:
2078:
2067:
2065:
2064:
2058:
2043:
2032:
2004:
2003:
2001:
2000:
1987:comp.dcom.modems
1974:
1968:
1967:
1960:"Serial (PC 25)"
1956:
1950:
1949:
1947:
1946:
1931:
1925:
1924:
1922:
1921:
1915:
1909:. Archived from
1900:
1891:
1885:
1884:
1858:
1852:
1851:
1849:
1848:
1834:
1828:
1827:
1806:
1800:
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1733:
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1709:
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1668:
1662:
1661:
1659:
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1643:
1637:
1636:
1635:
1634:
1619:
1602:
1585:
1398:
1323:
1322:
1245:Loopback testing
1150:distinctive ring
1090:
1068:
1013:Transmitted Data
967:Ready To Receive
808:
807:
681:pull-up resistor
607:Control circuits
601:
597:
526:operating system
518:headless systems
351:
343:ITU-T/CCITT V.28
333:
325:ITU-T/CCITT V.24
156:, data storage,
21:
2217:
2216:
2212:
2211:
2210:
2208:
2207:
2206:
2172:
2171:
2157:
2145:
2143:
2128:
2120:
2118:
2101:
2093:
2091:
2087:
2076:
2070:
2062:
2060:
2056:
2041:
2035:
2029:
2013:
2011:Further reading
2008:
2007:
1998:
1996:
1975:
1971:
1958:
1957:
1953:
1944:
1942:
1936:"Serial Wiring"
1932:
1928:
1919:
1917:
1913:
1898:
1892:
1888:
1873:
1859:
1855:
1846:
1844:
1836:
1835:
1831:
1824:
1814:Microsoft Press
1808:
1807:
1803:
1796:
1765:
1761:
1749:, Newnes, 2004
1744:
1740:
1731:
1729:
1717:
1716:
1712:
1703:
1701:
1696:
1695:
1691:
1670:
1669:
1665:
1656:
1654:
1645:
1644:
1640:
1632:
1630:
1620:
1605:
1595:Wayback Machine
1586:
1579:
1574:
1562:
1550:logic analyzers
1512:
1424:plug-compatible
1393:
1386:
1318:
1277:
1247:
1238:
1230:
1221:
1178:
1172:
1115:
944:Request To Send
834:Typical purpose
783:
751:Gender changers
735:
729:
689:
571:
542:
530:embedded system
457:
451:
394:
345:
327:
271:teletypewriters
259:
186:
35:
28:
23:
22:
15:
12:
11:
5:
2215:
2205:
2204:
2199:
2194:
2189:
2184:
2170:
2169:
2156:
2155:External links
2153:
2152:
2151:
2126:
2099:
2068:
2033:
2027:
2012:
2009:
2006:
2005:
1969:
1951:
1940:A. P. Lawrence
1926:
1886:
1871:
1853:
1829:
1822:
1801:
1794:
1772:Hill, Winfield
1768:Horowitz, Paul
1759:
1738:
1710:
1689:
1663:
1638:
1603:
1576:
1575:
1573:
1570:
1569:
1568:
1561:
1558:
1528:characters in
1525:logic analyzer
1511:
1508:
1499:
1498:
1492:
1489:
1483:
1473:
1467:
1461:
1455:
1449:
1440:
1402:receivers and
1385:
1382:
1379:
1378:
1375:
1371:
1370:
1367:
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1359:
1355:
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1346:
1343:
1339:
1338:
1335:
1331:
1330:
1327:
1317:
1314:
1276:
1275:Timing signals
1273:
1246:
1243:
1237:
1234:
1229:
1226:
1220:
1217:
1171:
1168:
1137:Ring Indicator
1130:telephone line
1114:
1113:Ring Indicator
1111:
1100:
1099:
1096:
1093:
1088:
1085:
1082:
1078:
1077:
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987:
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951:
948:
945:
941:
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937:
934:
931:
928:
925:
922:
921:Ring Indicator
918:
917:
914:
911:
908:
905:
902:
899:
898:Data Set Ready
895:
894:
891:
888:
885:
882:
879:
876:
870:
869:
866:
863:
860:
857:
854:
851:
845:
844:
841:
838:
835:
832:
828:
827:
826:pin (TIA-574)
821:
815:
812:
782:
779:
771:gender changer
764:Ring Indicator
731:Main article:
728:
725:
697:D-subminiature
688:
685:
634:
633:
630:
627:
623:
622:
619:
616:
612:
611:
608:
605:
570:
569:Voltage levels
567:
541:
538:
453:Main article:
450:
447:
446:
445:
442:
435:
420:
416:
409:
406:
403:
393:
390:
389:
388:
385:
382:
379:
376:
373:
370:
367:
364:
286:breakout boxes
258:
255:
227:
226:
223:
220:
217:
204:, timing, and
185:
182:
26:
9:
6:
4:
3:
2:
2214:
2203:
2200:
2198:
2197:EIA standards
2195:
2193:
2190:
2188:
2185:
2183:
2180:
2179:
2177:
2167:
2163:
2159:
2158:
2141:
2137:
2133:
2132:
2127:
2116:
2112:
2108:
2107:Knowledgebase
2104:
2100:
2086:
2082:
2075:
2074:
2069:
2055:
2051:
2047:
2040:
2039:
2034:
2030:
2024:
2020:
2015:
2014:
1995:
1992:
1988:
1984:
1980:
1973:
1965:
1961:
1955:
1941:
1937:
1930:
1916:on 2010-01-06
1912:
1908:
1904:
1897:
1890:
1882:
1878:
1874:
1868:
1864:
1857:
1843:
1839:
1833:
1825:
1823:1-57231-381-1
1819:
1815:
1811:
1805:
1797:
1795:0-521-37095-7
1791:
1787:
1783:
1779:
1778:
1773:
1769:
1763:
1757:, pages 41-42
1756:
1752:
1748:
1742:
1728:
1724:
1720:
1714:
1699:
1693:
1685:
1681:
1677:
1673:
1667:
1652:
1651:This Old Mill
1648:
1642:
1628:
1627:
1618:
1616:
1614:
1612:
1610:
1608:
1600:
1596:
1592:
1589:
1584:
1582:
1577:
1567:
1564:
1563:
1557:
1555:
1554:oscilloscopes
1551:
1547:
1543:
1539:
1535:
1531:
1526:
1522:
1518:
1507:
1504:
1496:
1493:
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1471:
1468:
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1448:
1444:
1441:
1439:
1435:
1432:
1431:
1430:
1427:
1425:
1420:
1416:
1413:A 20 mA
1411:
1409:
1405:
1404:depth finders
1401:
1396:
1391:
1376:
1373:
1372:
1368:
1365:
1364:
1360:
1357:
1356:
1352:
1349:
1348:
1344:
1341:
1340:
1336:
1334:Common Ground
1333:
1332:
1328:
1325:
1324:
1321:
1313:
1311:
1307:
1303:
1298:
1294:
1291:
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1272:
1270:
1265:
1263:
1262:
1255:
1252:
1242:
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1216:
1213:
1211:
1205:
1201:
1199:
1193:
1190:
1185:
1183:
1177:
1167:
1165:
1160:
1158:
1153:
1151:
1145:
1142:
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1131:
1127:
1123:
1119:
1110:
1107:
1094:
1086:
1079:
1075:
1072:
1064:
1059:Common Ground
1057:
1053:
1050:
1047:
1044:
1041:
1036:Received Data
1034:
1030:
1027:
1024:
1021:
1018:
1011:
1007:
1004:
1001:
998:
995:
990:Clear To Send
988:
984:
981:
978:
975:
972:
965:
961:
958:
955:
952:
949:
942:
938:
935:
932:
929:
926:
919:
915:
912:
909:
906:
903:
896:
892:
889:
886:
883:
880:
875:
871:
867:
864:
861:
858:
855:
850:
846:
842:
839:
836:
830:
829:
825:
819:
809:
806:
804:
795:
787:
778:
776:
773:is in use, a
772:
767:
765:
761:
756:
752:
748:
743:
741:
734:
724:
722:
718:
713:
711:
707:
703:
698:
693:
684:
682:
676:
674:
670:
666:
660:
656:
654:
649:
645:
641:
631:
628:
625:
624:
620:
617:
614:
613:
609:
606:
604:Data circuits
603:
602:
596:
594:
584:
575:
566:
564:
559:
555:
551:
547:
537:
535:
531:
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344:
340:
335:
331:
326:
322:
318:
314:
310:
304:
302:
298:
294:
289:
287:
283:
282:POS terminals
278:
276:
272:
268:
264:
254:
252:
248:
244:
240:
236:
232:
224:
221:
218:
215:
211:
210:short-circuit
207:
203:
199:
195:
194:
193:
191:
181:
178:
174:
170:
166:
161:
159:
155:
154:computer mice
151:
147:
142:
140:
139:serial cables
136:
131:
129:
125:
121:
118:), such as a
117:
116:
111:
110:
105:
101:
97:
93:
92:
87:
83:
79:
75:
71:
67:
60:(DTE) network
59:
55:
51:
44:
39:
33:
19:
2168:at Wikibooks
2144:. Retrieved
2130:
2119:. Retrieved
2106:
2092:. Retrieved
2072:
2061:. Retrieved
2045:
2037:
2018:
1997:. Retrieved
1972:
1964:Pinout Guide
1963:
1954:
1943:. Retrieved
1939:
1929:
1918:. Retrieved
1911:the original
1902:
1889:
1862:
1856:
1845:. Retrieved
1842:www.tldp.org
1841:
1832:
1809:
1804:
1776:
1762:
1746:
1741:
1730:. Retrieved
1722:
1713:
1702:. Retrieved
1692:
1671:
1666:
1655:. Retrieved
1653:. 2017-03-28
1650:
1641:
1631:, retrieved
1625:
1598:
1513:
1500:
1428:
1415:current loop
1412:
1387:
1319:
1299:
1295:
1286:
1281:clock signal
1278:
1266:
1259:
1256:
1248:
1239:
1231:
1222:
1214:
1206:
1202:
1198:flow control
1194:
1186:
1179:
1164:wake-on-ring
1161:
1154:
1146:
1136:
1135:
1103:
837:Abbreviation
800:
768:
747:breakout box
744:
736:
733:Serial cable
717:current loop
714:
694:
690:
677:
661:
657:
637:
632:−15 to −3 V
621:+3 to +15 V
589:
558:asynchronous
543:
515:
503:servo drives
492:
471:
470:In the book
469:
432:flow control
395:
358:
354:
336:
316:
305:
290:
279:
266:
260:
247:logic levels
228:
198:logic levels
187:
162:
143:
135:serial ports
132:
127:
113:
107:
103:
94:) such as a
89:
85:
69:
63:
1784:. pp.
1755:07506 5807X
1495:EIA/TIA-694
1486:EIA/TIA-562
1476:EIA/TIA-561
1464:MIL-STD-188
1426:equipment.
1271:(or BERT).
1132:was ringing
665:ground loop
648:charge pump
644:line driver
563:full duplex
554:synchronous
546:time-series
532:(such as a
464:PCI Express
455:Serial port
424:Handshaking
346: [
328: [
265:(EIA) as a
214:capacitance
32:serial port
2176:Categories
2146:2017-03-05
2121:2017-03-05
2094:2017-03-05
2063:2017-03-05
1999:2014-02-03
1945:2011-07-28
1920:2011-07-28
1881:1090438548
1847:2020-01-01
1732:2011-07-28
1704:2011-07-28
1657:2023-06-08
1633:2017-03-04
1572:References
1517:"Y" cables
1397:-compliant
1390:TTL levels
1152:patterns.
1122:USRobotics
775:null modem
687:Connectors
629:Deasserted
413:Null modem
402:interface.
56:(DCE) and
1983:Newsgroup
1723:About TIA
1395:NMEA 0183
814:Direction
760:crosstalk
653:slew rate
615:0 (space)
479:Microsoft
323:standard
251:bit rates
206:slew rate
202:baud rate
76:232 is a
2140:Archived
2115:Archived
2085:Archived
2054:Archived
1816:. 1997.
1774:(1989).
1684:38637094
1591:Archived
1560:See also
1261:loopback
1251:loopback
1182:Bell 202
1109:ground.
626:1 (mark)
618:Asserted
610:Voltage
520:such as
337:Related
173:Ethernet
150:printers
102:, and a
78:standard
1991:Usenet:
1985::
1786:723–726
1623:1976),
1470:EIA-530
811:Circuit
552:. Both
522:servers
428:dial-up
301:console
257:History
18:RS-232C
2025:
1993:
1879:
1869:
1820:
1792:
1753:
1682:
1544:, and
1458:RS-485
1452:RS-449
1443:RS-423
1434:RS-422
1408:MAX232
1326:Signal
1308:, and
1189:RS-485
1091:Common
1069:Common
740:RS-422
727:Cables
702:DB-25M
673:RS-485
669:RS-422
578:order.
534:router
505:, and
239:EBCDIC
233:(i.e.
169:RS-485
165:RS-422
124:pinout
70:RS-232
2088:(PDF)
2077:(PDF)
2057:(PDF)
2042:(PDF)
1914:(PDF)
1899:(PDF)
1542:DDCMP
1530:ASCII
1192:bus.
1126:DB-25
818:DB-25
706:DE-9M
511:DE-9M
473:PC 97
350:]
339:ITU-T
332:]
321:CCITT
235:ASCII
120:modem
43:DB-25
2023:ISBN
1877:OCLC
1867:ISBN
1818:ISBN
1790:ISBN
1751:ISBN
1680:OCLC
1552:and
1546:X.25
1538:HDLC
1534:SDLC
1501:The
1329:Pin
1310:X.25
1306:HDLC
1302:SDLC
843:DCE
831:Name
824:DE-9
820:pin
755:8P8C
556:and
550:bits
439:mice
422:The
419:use.
297:PLCs
243:UART
188:The
171:and
137:and
1599:EIA
1400:GPS
1377:12
1369:13
1361:19
1353:16
1345:14
1264:).
1065:GND
1048:Out
1042:RxD
1022:Out
1019:TxD
1002:Out
996:CTS
976:Out
973:RTR
953:Out
950:RTS
936:22
933:Out
910:Out
904:DSR
887:Out
881:DCD
865:20
859:Out
856:DTR
840:DTE
766:).
671:or
548:of
483:USB
299:),
177:USB
112:or
104:DCE
98:or
86:DTE
72:or
64:In
2178::
2134:.
2113:.
2109:.
2105:.
2079:.
2044:.
1989:.
1981:.
1962:.
1938:.
1905:.
1901:.
1875:.
1840:.
1788:.
1770:;
1725:.
1721:.
1649:.
1606:^
1580:^
1540:,
1536:,
1312:.
1304:,
1200:.
1098:—
1095:1
1087:PG
1076:5
1073:7
1054:2
1051:3
1045:In
1031:3
1028:2
1025:In
1008:8
1005:5
999:In
985:7
982:4
979:In
962:7
959:4
956:In
939:9
930:In
927:RI
916:6
913:6
907:In
893:1
890:8
884:In
868:4
862:In
501:,
497:,
477:,
348:de
330:de
237:,
200:,
167:,
152:,
100:PC
68:,
41:A
2149:.
2124:.
2097:.
2066:.
2031:.
2002:.
1966:.
1948:.
1923:.
1883:.
1850:.
1826:.
1798:.
1735:.
1707:.
1686:.
1660:.
1601:)
441:.
216:.
106:(
88:(
34:.
20:)
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