Interface Between Data Terminal Equipment and Data Circuit Terminating Equipment Employing Serial Binary Data Interchange
[RS232 Description] [RS232
Standard Organizations]
[RS232 Interface ICs] [RS232
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The RS232 specification defines both the Mechanical, Electrical, and
Functional characteristics of the interface.
RS232 is an Unbalanced (Single Ended),
unidirectional (point-to-point) interface, with the signal referenced to
ground.
RS232 drivers feature a controlled slew rate. Normal output
levels are +5 volts.
The RS-232 interface uses Asynchronous Framing [Known data
width, 8bits] with NRZ encoding.
The RS232 interface is synchronous when the clocks are used (DA / DB), otherwise its asynchronous.
The RS232 interface is rated to operate up to 20kbps. Use TIA/EIA-562 (low voltage version of RS232) or
TIA/EIA 423 for higher data rates. |
The stop bit is used to bring [or insure] the signal rests at a logic high following the end of the frame; so when the next start bit arrives it will bring the bus from a high to low ~ remember we will invert, so on the RS232 cable the stop bit is low and the start bit will transition low to high. Remember TIA/EIA232 does not define the protocol or parity.
EIA-232 Cable Distance vs. Bus Speed
Graph extracted from a Texas Instruments Application note
EIA/TIA-232-F Interface Between Data Terminal Equipment and Data
Circuit Terminating Equipment Employing Serial Binary Data
Interchange
EIA/TIA-561 8 Position Non-Synchronous Interface Between Data
Terminal Equipment and Data Circuit Terminating Equipment Employing
Serial Binary Data Interchange
EIA/TIA-574 9 Position Non-Synchronous Interface Between Data
Terminal Equipment and Data Circuit Terminating Equipment Employing
Serial Binary Data Interchange
Telecommunications Industry Association; TIA [www.tiaonline.org]
Note the Electronic Industries Alliance {EIA} ceased operations on Feb 22 2011.
V.28: Electrical characteristics for unbalanced double-current interchange circuits
ITU {International Telecommunication Union}, www.itu.int
TIA/EIA-694 is another electrical standard which is very similar to TIA/EIA-232-F, but supports higher data rates (512 kbps). It is an electrical only standard, which is intended to be referenced by complete standards, such as TIA/EIA-723. TIA/ EIA-694 specifies an unbalanced, unidirectional, point-to-point interface. This standard supports interoperability with TIA/EIA-232-F devices.
MIL-STD-188C [Military Standard 188C] is similar to TIA/ EIA-232-F as an unbalanced point-to-point interface. MIL-STD-188C uses a maximum driver output of 7 volts.
EIA-334-A defines signal quality terms for synchronous serial
DTE/DCE interfaces. This standard is referenced by the complete
synchronous standards.
EIA-363 defines signal quality terms for non-synchronous serial
DTE/DCE interfaces. This standard is referenced by the complete
non-synchronous standards.
EIA-404-A defines signal quality for start-stop non-synchronous
DTE/DCE interfaces.
RS232 Pinout:
The RS232 specification only defines the pin-out for a 25 pin D-sub connector;
however, the 9 pin is used more often (defined by EIA-574).
A 26 pin connector is also called out in the RS232 spec.
EIA-561 calls out an 8 pin connector (RJ-45).
RS232C indicates a DB25, RS232D indicates an RJ45.
Although this site, in general, calls out DB9 and DB25 style connectors, the real term
for a 9-pin D-sub is DE9.
A listing of Dsub connector manufacturers is
listed on the D-Sub
Connector Manufacturers page.
D-Sub
Shell Dimensions,
D-Sub
Insert Arrangements.
Many RS232 pinouts listed here are also listed on the RS232 Pinout page.
An RS232 Pin out table may also be termed RS232 Signal Assignments.
Pin # | Signal name | Signal Description |
1 | CD | Carrier Detect |
2 | RXD | Receive Data |
3 | TXD | Transmit Data |
4 | DTR | Data Terminal Ready |
5 | GND | Signal Ground / Common |
6 | DSR | Data Set Ready |
7 | RTS | Request To Send |
8 | CTS | Clear To Send |
9 | RI | Ring Indicator |
Pin # | Signal name | Signal Function | Pin # | Signal name | Signal Function |
1 | ---- | Protective Ground | 14 | SBA | 2nd Transmitted Data |
2 | TXD | Transmitted Data | 15 | DB | DCE Element Timing |
3 | RXD | Receive Data | 16 | SBB | 2nd Received Data |
4 | RTS | Request To Send | 17 | DD | Received Element Timing |
5 | CTS | Clear To Send | 18 | ----- | Unassigned |
6 | DSR | Data Set Ready | 19 | SCA | 2nd Request To Send |
7 | GND | Signal Ground/Common | 20 | DTR | Data Terminal Ready |
8 | CD | Carrier Detect | 21 | CG | Signal Quality Detector |
9 | --- | +Voltage | 22 | RI | Ring Detector |
10 | --- | -Voltage | 23 | CH/CI | Data Signal Rate Detector |
11 | --- | ---- | 24 | DA | DTE Element Timing |
12 | SCF | 2nd Line Detector | 25 | ---- | Unassigned |
13 | SCB | 2nd Clear To Send | -- | --- | --- |
Pin # | Signal name | Signal Description |
1 | RI | Ring Indicator |
2 | DCD | Carrier Detect |
3 | DTR | Data Terminal Ready |
4 | GND | Signal Ground / Common |
5 | RXD | Receive Data |
6 | TXD | Transmit Data |
7 | CTS | Clear To Send |
8 | RTS | Request To Send |
DB9, DTE | RJ45 | DB9, DCE | *** | DB25 | RJ45 | DB9 | ||||||
Pin | Signal | Pin | Signal | Pin | Signal | Pin | Signal | Pin | Signal | Pin | Signal | |
7 | RTS | 1 | DCD | 1 | DCD | 4 | RTS | 1 | DCD | 7 | RTS | |
8 | CTS | 2 | RTS | 7 | RTS | N/A | N/A | 2 | N/A | N/A | N/A | |
Shell | GND | 3 | GND | Shell | GND | Shell | GND | 3 | GND | Shell | GND | |
3 | RxD | 4 | TxD | 3 | TxD | 3 | RxD | 4 | TxD | 2 | RxD | |
2 | TxD | 5 | RxD | 2 | RxD | 2 | TxD | 5 | RxD | 3 | TxD | |
5 | GND | 6 | GND | 5 | GND | 7 | GND | 6 | GND | 5 | GND | |
4 | DTR | 7 | CTS | 8 | CTS | N/A | N/A | 7 | N/A | N/A | N/A | |
6 | DSR | 8 | DTR | 4 | DTR | N/A | N/A | 8 | N/A | N/A | N/A | |
RJ45 to DTE, DB9 | N/A | RJ45 to DB25 | N/A | |||||||||
N/A | RJ45 to DCE, DB9 | N/A | RJ45 to DB9 | |||||||||
@ 8 wire 8 pin RJ45 | @ 4 wire 8 pin RJ45 |
RJ45 to DB25 Adapter |
Computers or peripherals which use serial cables for their communication
are split into two categories. These are DCE (Data Communications
Equipment) and DTE (Data Terminal Equipment.) Data Communications
Equipment are peripheral devices such as a modem, or plotter while Data
Terminal Equipment is the Computer or Terminal. |
Pin # | Signal name | Signal Description | Cable | Pin # | Signal name | Signal Description |
2 | RXD | Receive Data | Cross | 3 | TXD | Transmit Data |
3 | TXD | Transmit Data | Cross | 2 | RXD | Receive Data |
4 | RTS | Request To Send | Cross | 5 | CTS | Clear To Send |
5 | CTS | Clear To Send | Cross | 4 | RTS | Request To Send |
6 | DSR | Data Set Ready | Cross | 20 | DTR | Data Terminal Ready |
7 | GND | Ground | Cross | 7 | GND | Ground |
8 | CD | Carrier Detect | Cross | 20 | DTR | Data Terminal Ready |
20 | DTR | Data Terminal Ready | Cross | 6 | DSR | Data Set Ready |
20 | DTR | Data Terminal Ready | Cross | 8 | CD | Carrier Detect |
The serial port found on a Personal Computer uses either a 9-pin D or
25-pin D connector. The pinout for both those connector types is listed
above.
This page also lists both of these connector types as they relate
to the Personal Computer; RS232 pinout. Serial cables are longer then
parallel cables because of the data transmission used.
EIA-562: Electrical Characteristics for an Unbalanced Digital
Interface
EIA-562 or TIA-562 is the low voltage version of the RS232 standard.
EIA-562 operates at 20kbps over a single-ended line just as RS232
does.
How ever; EIA562 has a minimum output of +/- 3.7 volts, and a maximum
output of +/- 25 volts.
The TIA/EIA-562 specification does allow for
inter-operation with RS232.
RS232 Dual I/O Chip |
RS232 Manufacturers |
Government Specifications [Standard Microcircuit Drawing]
5962-06207; Microcircuit, Digital-Linear, 3 V, RS-232, Receiver / Transmitter Transceiver with Shutdown [2,3, or 5 receivers]
5962-87666; Microcircuit, Linear, Dual RS232 Transceivers [LT1080MJ/883]
5962-89877; Microcircuit, Linear, CMOS, Dual, RS232, Transceiver [MAX232, MAX230, MAX231, MAX234, MAX236]
5962-91729; Microcircuits, Linear, Dual RS-232 Transceiver [LT1180, LT1181]
5962-94565; Microcircuit, Linear, Driver/Receiver, Dual, RS-232, CMOS [MAX220, MAX220, MAX242, MAX243]
A common design consideration is the protection of the I/O lines leading to the interface ICs. Two common methods are to use protection diodes or TVS components. A number of different TVS part numbers in two different package configurations is shown on the TVS DIP Components page. Steering diodes may be also be used to protect the data lines from voltage spike and surges. Three different circuit configurations in two different package options are provided; Diode Array in a DIP Package, Diode Array in a Flat Package.
IC Manufacturers {All other Integrated Circuit device types}
The RS232 standard does not define a cable, just the cable capacitance and two different forms of connectors. Much of the color coding information found on the internet is based on different equipment using RS232 interfaces. So one page may show one RS232 color code while another shows a completely different one. Of course many pages also may just be copies of some other page. In some cases when an RS232 cable is used to translate to another interface, than that interface standard might be used as the wiring color code for the cable. However, any color coding used with RS232 will be non-standard. If connecting to a legacy system, or wiring to a design standard use that RS232 pinout color coding scheme. Otherwise use a multiconductor or multipair, shielded or unshielded 'data cable' that contains either 24 or 26 AWG wires and use the color code that comes with the cable. Note the wire color codes normally change with the number of individual wires contained in the cable. A Data Grade Cable is a category of cable. Of course the example RS232 interface card to the right uses no color coding at all, just a red strip to indicate pin 1. |
RS232, Expansion Card |
RS232 usage continues to decline. |
RS232, Google Search Trend, 2004 to 2010 |
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