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Wednesday, April 30, 2014

DTE & DCE / DB25 & DB9 Port

DTE & DCE / DB25 & DB9 Port


Let's talk about DCE (Data Communications Equipment) and DTE (Data Terminal Equipment) devices. The difference between DCE and DTE is largely in the Plug and the direction if each pin (input or output). Your desktop PC is termed as a DTE device.
DCE devices use a 25-pin female connector while a DTE device uses a 25 pin male connector. Also, complimentary signals lines like transmit and receive are "swapped" between the two types. Thus, a straight-through cable can be used to connect a DCE device to a DTE device.
DTEDCE
25 pin Male pinout25 pin Female pinout
Pin 1 - Shield GroundPin 1 - Shield Ground
Pin 2 - Transmitted Data (TD) outputPin 2 - Transmitted Data (TD) input
Pin 3 - Receive Data (RD) inputPin 3 - Receive Data (RD) output
Pin 4 - Request To Send (RTS) outputPin 4 - Request To Send (RTS) input
Pin 5 - Clear To Send (CTS) inputPin 5 - Clear To Send (CTS) output
Pin 6 - Data Set Ready (DSR) inputPin 6 - Data Set Ready (DSR) output
Pin 7 - Signal GroundPin 7 - Signal Ground
Pin 8 - Carrier Detect (CD) inputPin 8 - Carrier Detect (CD) output
Pin 20 - Data Terminal Ready (DTR) outputPin 20 - Data Terminal Ready (DTR) input
Pin 22 - Ring Indicator (RI) inputPin 22 - Ring Indicator (RI) output
You can effectively convert DCE/DTE devices by using a NULL Modem cable. The null modem cable swaps the complimentary signals and allows a DCE device to act like a DTE and vice-versa.
The following chart depicts the cabling of the DB9 connector found on an IBM-PC type computer.
DTE
9 pin Male pinout
Pin 1 - Carrier Detect (CD) input
Pin 2 - Receive Data (RD) input
Pin 3 - Transmitted Data (TD) output
Pin 4 - Data Terminal Ready (DTR) output
Pin 5 - Signal Ground
Pin 6 - Data Set Ready (DSR) input
Pin 7 - Request To Send (RTS) output
Pin 8 - Clear To Send (CTS) input
Pin 9 - Ring Indicator (RI) input

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