Serial Cable Pinouts

Pinout List For RS-232 Serial Cables

DB-25

DB-9

Circuit

Function

-----

AA

Chassis Ground

2

3

BA

Transmitted Data

3

2

BB

Received Data

4

7

CA

Request To Send

5

8

CB

Clear To Send

6

6

CC

Data Set Ready

7

5

AB

Signal Ground

8

1

CF

Carrier Detect

12

-----

SCF

Speed Indicate

20

4

CD

Data Terminal Ready

22

 9

CE

Ring Indicate

The Minimum required pins needed for the modem to operate are: Data, Signal Ground and Data Terminal Ready (unless DIP 1 is down).

Also, the sources of the signal are:
1 and 7 are supplied by both the Terminal and the Modem
2,4,20 are supplied by the Terminal
3,5,6,8,12,22 are supplied by the Modem

For a Macintosh 8-pin DIN:

DB-25

Macintosh

2

3

Transmitted Data

3

5

Received Data

4

1

Request To Send

5

2

Clear To Send

7

4

Ground

20

1

Data Terminal Ready

Note: On a Mac, the DTR is tied to the RTS line. This makes it necessary to override DTR(dip 1 down).