Copyright © 2010 Future Technology Devices International Limited

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Document Reference No.: FT_000204

DB9-USB-RS232 Datasheet

Version 1.2

Clearance No.: FTDI# 130

Appendix B – DCE and DTE Wire Configurations

This section is included for reference when designing a PCB for a DB9-USB-RS232 module; here some of

the subtle details of DTE and DCE wire configurations will be outlined.

B.1 Wire Configuration for the Male and Female Modules

When designing a PCB for the DB9-USB-RS232 module consideration should be given to Data Terminal

Equipment (DTE) and Data Communication Equipment (DCE) connection standards. The DB9-USB-RS232

modules are designed as a DTE device. When a DTE devices is being connected to the DB9-USB-RS232 a

“null-modem” wiring is used, when the DB9-USB-RS232 is connected to a DCE a “straight through” wiring

is used. The expressions “null-modem” and “straight through” are explained in the next subsection.

The male DB9-USB-RS232-M module is designed to replace a male DB9 connector of a DTE device

(according to TIA standards Male DB9 connectors are to be used only with wiring DTE to UART). The

female DB9-USB-RS232-F module is designed to replace a female DB9 connector of a DCE device

(according to TIA standards Female DB9 connectors are to be used only with wiring DCE to UART).

B.1.1 RS232 Wiring

RS232 cables have followed a standard 9-pin configuration on a D-sub connector since the mid 1980s.

The DB9-USB-RS232-M modules are DTE devices. To connect a DB9-USB-RS232 module to a DCE device,

a “straight-through” wiring scheme, as described in Table B.1, needs to be used.

DTE Pin Number

Signal Name

DCE Pin Number

1

DCD = Data Carrier Detect

1

2

RXD = Receive Data

2

3

TXD = Transmit Data

3

4

DTR = Data Terminal Ready

4

5

GND = RS232 signal ground

5

6

DSR = Data Set Ready

6

7

RTS = Request To Send

7

8

CTS = Clear To Send

8

9

RI = Ring Indicator

9

Table B.1 – RS232 DTE to DCE connection with straight-through wiring

To connect a DB9-USB-RS232 module to a DCE device, a “null-modem” wiring scheme, as described in

Table B.2 needs to be used.