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DB-25 Connector
The DB-25 connector (named for its "B"-size "D"-shaped
shell and 25 pins) is practically ubiquitous in the electronics industry. The DB-25 connector is used for a variety of purposes. Two common
applications are RS-232/EIA-232 (serial) connections, and the parallel printer interface
on the IBM PC. The DB-25 connector is also used for SCSI
connections.
Here's a good set of figures for DB-25 male and female connectors, as viewed
from the pin side (not the solder side).
DB-25 Male
DB-25 Female
Pins commonly used for RS-232/EIA-232 (serial):
| DB-25 |
DB-9 |
Signal Direction |
Signal Name |
| 1 |
|
x |
Protective Ground |
| 2 |
3 |
DTE-to-DCE |
Transmitted Data |
| 3 |
2 |
DCE-to-DTE |
Received Data |
| 4 |
7 |
DTE-to-DCE |
Request To Send |
| 5 |
8 |
DCE-to-DTE |
Clear To Send |
| 6 |
6 |
DCE-to-DTE |
Data Set Ready |
| 7 |
5 |
x |
Signal Ground |
| 8 |
1 |
DCE-to-DTE |
Received Line Signal Detector (Carrier Detect) |
| 20 |
4 |
DTE-to-DCE |
Data Terminal Ready |
| 22 |
9 |
DCE-to-DTE |
Ring Indicator |
Click here to see the pinout of D-sub 9
connectors.
Common Null-Modem Connection
|
Signal Name
|
DB-25 Pin
|
D-sub 9 Pin
|
|
D-sub 9 Pin
|
DB-25 Pin
|
|
| FG (Frame Ground) |
1 |
- |
X |
- |
1 |
FG |
| TD (Transmit Data) |
2 |
3 |
- |
2 |
3 |
RD |
| RD (Receive Data) |
3 |
2 |
- |
3 |
2 |
TD |
| RTS (Request To Send) |
4 |
7 |
- |
8 |
5 |
CTS |
| CTS (Clear To Send) |
5 |
8 |
- |
7 |
4 |
RTS |
| SG (Signal Ground) |
7 |
5 |
- |
5 |
7 |
SG |
| DSR (Data Set Ready) |
6 |
6 |
- |
4 |
20 |
DTR |
| CD (Carrier Detect) |
8 |
1 |
- |
4 |
20 |
DTR |
| DTR (Data Terminal Ready) |
20 |
4 |
- |
6 |
6 |
DSR |
| DTR (Data Terminal Ready) |
20 |
4 |
- |
1 |
8 |
CD |
Click here to see the pinout of DB-9
connectors.
DB-25 pins commonly used for the IBM-PC parallel port:
| DB-25 Pin |
Centronics Pin |
Signal Description |
Signal Direction
(at the PC) |
Signal Function |
| 1 |
1 |
STROBE |
Output |
Clocks data |
| 2 |
2 |
DATA Bit 0 |
Output |
Data line |
| 3 |
3 |
DATA Bit 1 |
Output |
Data line |
| 4 |
4 |
DATA Bit 2 |
Output |
Data line |
| 5 |
5 |
DATA Bit 3 |
Output |
Data line |
| 6 |
6 |
DATA Bit 4 |
Output |
Data line |
| 7 |
7 |
DATA Bit 5 |
Output |
Data line |
| 8 |
8 |
DATA Bit 6 |
Output |
Data line |
| 9 |
9 |
DATA Bit 7 |
Output |
Data line |
| 10 |
10 |
ACKNLG |
Input |
Acknowledge receipt of data |
| 11 |
11 |
BUSY |
Input |
Printer is busy |
| 12 |
12 |
POUT |
Input |
Printer is out of paper |
| 13 |
13 |
SEL |
Input |
Pinter is online |
| 14 |
14 |
Auto Feed XT |
Output |
Autofeed |
| 15 |
32 |
FAULT |
Input |
Indicates printer fault (or when printer is offline) |
| 16 |
31 |
Input Prime or INIT |
Output |
Resets printer, clears printer buffer and initializes it |
| 17 |
36 |
SLCT IN |
Output |
TTL high level |
| 18-25 |
16, 17, 19-30, 33 |
Ground |
N/A |
Ground reference for signal pins 1-12, in most cables as
twisted pairs. |
Click here to see the pinout of
Centronics
connectors.
DB-25 pins commonly used for SCSI
At one time, Apple used a DB25 connector for SCSI (narrow), but
this doesn't allow twisted pairs and is not compliant to SCSI standards. Some
companies like Iomega still use this connector on new devices. Such
connectors have been noted to have problems on SCSI busses using faster devices
such as UltraSCSI (Iomega itself doesn't recommend using more than one DB25
device, but still uses it for Zip drives). The HD50 connector is preferred.
| DB-25 Pin |
LD-50 Centronics Pin |
Signal Description |
Signal Function |
| 1 |
49 |
REQ |
Request |
| 2 |
46 |
MSG |
Message |
| 3 |
50 |
I/O |
Input/Output |
| 4 |
45 |
RST |
Reset |
| 5 |
44 |
ACK |
Acknowledge |
| 6 |
43 |
BSY |
Busy |
| 7, 9, 14, 16, 18, 24 |
1-11, 15-25, 35, 36, 40, 42 |
GND |
Ground |
| 8 |
26 |
D0 |
Data bit 0 |
| 10 |
29 |
D3 |
Data bit 3 |
| 11 |
31 |
D5 |
Data bit 5 |
| 12 |
32 |
D6 |
Data bit 6 |
| 13 |
33 |
D7 |
Data bit 7 |
| 15 |
48 |
C/D |
Command / -Data |
| 17 |
41 |
ATN |
Attention |
| 19 |
47 |
SEL |
Select |
| 20 |
34 |
DP |
Data Parity |
| 21 |
27 |
D1 |
Data bit 1 |
| 22 |
28 |
D2 |
Data bit 2 |
| 23 |
30 |
D4 |
Data bit 4 |
| 25 |
38 |
TermPwr |
Termination Power (+5V) |
Click here to see the pinout of
Centronics connectors for SCSI.
You can find more SCSI info here.
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