
Chapter 1 – Product Description and Specifications
9-Pin Fem-D Sub Serial Connector
The following table explains the pin functions.
DE9 Pin Assignment
Female Connector
DE9
Pins
Pin 1
Pin 2
Pin 3
Pin 4
Pin 5
Pin 6
Pin 7
Pin 8
Pin 9
RS232 Signals
DCE
Data Carrier Detected (DCD)
RXD
TXD
Data Terminal Ready (DTR)
Ground
Data Set Ready (DSR)
Ready To Send (RTS)
Clear To Send (CTS)
Ring Indicator (RI)
RS422 Full
Duplex Signals
RxD-
RxD+
TxD+
TxD-
Ground
Ready To Send -
(RTS-)
Ready To Send +
(RTS+)
Clear To Send +
(CTS+)
Clear To Send -
(CTS-)
Signal
Direction
Out
Out
In
In
N/A
Out – RS232
In – RS422
In
Out
Out
Note: The DSR signal on pin 6 is always asserted by the modem.
4-Position DIP Switch
Switch Position
Position 1
Position 1
Positions 2-4
Position 2
Position 2
Position 3
Position 3
Position 4
Position 4
Up/On
Down/Off
Off
On
Off
On
Off
On
Off
On
Description
DTR Reset Disabled
DTR Reset Enabled
Only valid for serial builds
No TXD Termination
TXD Diff Pair Terminated
No RTS Termination
RTS Diff Pair Terminated
RS232 Mode
RS422 Mode
Note: Positions 2 and 3 should only be used in RS422 Mode. Enabling TXD/RTS termination may be required to avoid
errors at high bit rates or long cable lengths. Multi-Tech Systems tested the cable up to 1,000 feet , but the
maximum may be more with termination enabled and lower data rates.
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Multi-Tech Systems, Inc. MultiModem Cell User Guide