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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 Male

DB-25 Female

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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This site last updated 7/11/2008