Chapter 3: Port Connections; Dte/Dce Explanation - B&B Electronics 232BSS4 Manual

Chapter 3: PORT CONNECTIONS

DTE/DCE Explanation

232BSS4, it is necessary to have a basic understanding of the terms
DTE and DCE. RS-232 was designed, using DB-25 connectors, for
connecting a DTE (Data Terminal Equipment) device to a DCE (Data
Communication Equipment) device. Each device will have inputs on
pins that correspond to outputs on the same pins of the other device.
For example, a DTE device will transmit data out on pin 2 (on a DB-
25) and a DCE device will receive data in on pin 2 (on a DB-25). IBM
PCs and serial printers are DTE devices, modems are DCE devices.
connector. Since then, the use of a 9 pin D-Sub supporting only a
portion of the original RS-232 signals has been used extensively,
starting with the IBM PC and migrating into other peripherals. The
pinouts for this 9 pin connector have since become the EIA/TIA 574
standard. This standard specifies a DTE device that transmits on pin
3 and receives on pin 2, with the DCE having the opposite
configuration.
25 Pin DTE
20
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In order to determine the proper port connections to the
Originally the RS-232 standard specified only a 25 pin D-sub
25 Pin DCE
DEVICE LINE LINE
2 (TD) 2 (TD)
T
3 (RD) 3 (RD)
R
4 (RTS) 4 (RTS)
T
5 (CTS) 5 (CTS)
R
20 (DTR) 20 (DTR)
T
6 (DSR) 6 (DSR)
R
8 (DCD) 8 (DCD)
R
7 (GND) 7 (GND)
T = RS-232 Transmitter
Figure 3.1. DTE/DCE Port Diagrams
B&B Electronics Mfg Co Inc – 707 Dayton Rd - PO Box 1040 - Ottawa IL 61350 - Ph 815-433-5100 - Fax 815-433-5104
B&B Electronics Ltd – Westlink Commercial Park – Oranmore, Galway, Ireland – Ph +353 91-792444 – Fax +353 91-792445
9 Pin DTE
DEVICE DEVICE
R
T
T R
R
T
T R
R T
R
T
R
T
R = RS-232 Receiver
Documentation Number 232BSS41202 Manual
9 Pin DCE
LINE LINE DEVICE
3 (TD) 3 (TD)
R
2 (RD) 2 (RD)
T
7 (RTS) 7 (RTS)
R
8 (CTS) 8 (CTS)
T
4 (DTR) 4 (DTR)
R
6 (DSR) 6 (DSR)
T
1 (DCD) 1 (DCD)
T
5 (GND) 5 (GND)