RS-232
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RS-232
RS-232 is also known as EIA-232 and TIA-232E -- and even V.28/V.24 by the weirdos. These standards are not identical, but you will see them together. EIA/TIA also specifies various pinouts. In theory, the pure RS-232C standard only specifies the signaling, not how you actually wire it up.
The RS-232 standard requires the transmitter to use +12V (0, logic low) and -12V (1, logic high). The receiver needs only see over +3V and under -3V. Most transmitting ports use only +5V and -5V. Those levels are compatible with most devices and host computers. Maxim is one of the more popular suppliers of RS-232 level shifters or level converters.
D-sub 9 pinout (TIA-574, DE-9, and DB-9)
Technically this connector is called a D-sub 9 or a DE-9, but it is often called a DB-9 even though that refers to the wrong size. The D refers to the shape of the connector. The E specifies the size of the connector shell (E == subminiature).
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DB-25 pinout
The D refers to the shape of the connector. The B specifies the size of the connector shell. Note that DB-25 may carry two RS-232 lines. This is rare.
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3-wire RS-232
A minimal "3-wire" RS-232 connection consists only of TxD, RxD, and SGND (pins 3,2,5 on DB-9 and pins 2,3,7 on DB-25).
5-wire RS-232
A minimal RS-232 connection with hardware flow control: TxD, RxD, SGND, RTS, and CTS (pins 3,2,5,7,8 on DB-9 and pins 2,3,7,4,5 on DB-25).
RS-232 DB-25 to DB-9 Pinout table
DB-25 |
DB-9 |
line |
description |
direction DTE is the computer DCE is the device |
---|---|---|---|---|
1 |
shield |
ground shield |
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2 |
3 |
TxD |
Transmit Data |
OUT: DTE -> DCE |
3 |
2 |
RxD |
Receive Data |
IN: DTE <- DCE |
4 |
7 |
RTS |
Request To Send |
OUT: DTE -> DCE |
5 |
8 |
CTS |
Clear To Send |
IN: DTE <- DCE |
6 |
6 |
DSR |
Data Set Ready |
IN: DTE <- DCE |
7 |
5 |
SGND |
signal ground |
< - > |
8 |
1 |
DCD |
Data Carrier Detect |
IN: DTE <- DCE |
9 |
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10 |
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11 |
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12 |
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13 |
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14 |
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15 |
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16 |
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17 |
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18 |
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19 |
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20 |
4 |
DT |
Data Terminal Ready |
OUT: DTE -> DCE |
21 |
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22 |
9 |
Rind Indicator |
IN: DTE <- DCE | |
23 |
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24 |
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25 |