db9-usb-rs232 Future Technology Devices International Ltd., db9-usb-rs232 Datasheet - Page 25

• Manufacturer Part Number: db9-usb-rs232
• Description: Rs232 Connection
• Manufacturer: Future Technology Devices International Ltd.

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.
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.
Table B.1 – RS232 DTE to DCE connection with straight-through wiring
DTE Pin Number
Copyright © 2010 Future Technology Devices International Limited
1
2
3
4
5
6
7
8
9
DTR = Data Terminal Ready
GND = RS232 signal ground
DCD = Data Carrier Detect
RTS = Request To Send
DSR = Data Set Ready
TXD = Transmit Data
CTS = Clear To Send
RXD = Receive Data
RI = Ring Indicator
Signal Name
DCE Pin Number
1
2
3
4
5
6
7
8
9
Document Reference No.: FT_000204
DB9-USB-RS232 Datasheet
Clearance No.: FTDI# 130
Version 1.2
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