Edward Berner
3/4/2004

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Looking into a male DB25 connector, the pins are numbered from left to
right.  The top row is 1-13 and the bottom row 14-25.

    1. . . . . . . . . . . . .13
    14. . . . . . . . . . . .25

Looking into a female DB25 connector, the pins are numbered from right
to left.  The top row is 13-1 and the bottom row 25-14.

    13. . . . . . . . . . . . .1
     25. . . . . . . . . . . .14

DB25 pinout  (RS-232C)

Pin  Name  Function
---  ----  --------
  1  FG    Frame ground
  2  TD    Transmitted data
  3  RD    Received data
  4  RTS   Request to send
  5  CTS   Clear to send
  6  DSR   Data set ready
  7  SG    Signal ground
  8  DCD   Data carrier detect
  9        Positive test voltage
 10        Negative test voltage
 11  QM    Equalizer mode
 12  SDCD  Secondary data carrier detect
 13  SCTS  Secondary clear to send
 14  STD   Secondary transmitted data
 15  TC    Transmitter clock
 16  SRD   Secondary received data
 17  RC    Receiver clock
 18  DCR   Divided clock receiver
 19  SRTS  Secondary request to send
 20  DTR   Data terminal ready
 21  SQ    Signal quality detect 
 22  RI    Ring indicator
 23  DRS   Data rate selector
 24  SCTE  Serial clock transmit external
 25  BUSY  Busy

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DB9 pinout  (EIA/TIA 574)

Looking into a male DB9 connector, the pins are numbered thusly:

    1. . . . .5
     6. . . .9

Pin  Name  Function
---  ----  ---------
  1  DCD   Data carrier detect
  2  RD    Received data
  3  TD    Transmitted data
  4  DTR   Data terminal ready
  5  SG    Signal ground
  6  DSR   Data set ready
  7  RTS   Request to send
  8  CTS   Clear to send
  9  RI    Ring indicator

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Serial on RJ45 (EIA/TIA 561)

Looking at the front of an RJ45 plug with the clip down, the pins are
numbered from right to left.

    8........1

Looking into an RJ45 jack with the tabbed part down, the pins are
numbered from left to right.

    1........8


Pin  Name  Function
---  ----  --------
  1  RI    Ring indicator
  2  DCD   Data carrier detect
  3  DTR   Data terminal ready
  4  SG    Signal ground
  5  RD    Received data
  6  TD    Transmitted data
  7  CTS   Clear to send
  8  RTS   Request to send

(Compared to the DB9 pinout, the DSR signal is missing.)

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Cross Reference

Signal  RJ45
Name    (EIA 561)  DB9  DB25
------  ---------  ---  ----
RI          1       9    22
DCD         2       1     8
DTR         3       4    20
SG          4       5     7
RD          5       2     3
TD          6       3     2
CTS         7       8     5
RTS         8       7     4

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$Id: pinouts.txt,v 1.2 2007/01/03 18:00:25 erb Exp $