RS-232

RS-232

RS-232 is also known as EIA/TIA-232E and V.28/V.24. These are not identical, but you will see them together.

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 (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 this 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).

 1 2 3 4 5
  6 7 8 9

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.

 1  2  3  4  5  6  7  8  9 10 11 12 13
  14 15 16 17 18 19 20 21 22 23 24 25

3-wire

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
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
10
11
12
13
14
15
16
17
18
19
20	4	DT	Data Terminal Ready	OUT: DTE -> DCE
21
22	9		Rind Indicator	IN: DTE <- DCE
23
24
25