US Robotics COURIER User Manual page 113

COURIER HIGH SPEED MODEMS
THE RS-232 INTERFACE
DESCRIPTION
The RS-232 interface is a standard developed by the Electronic
Industries Association (EIA).
It
defines the signals and voltages
used when data is exchanged between a computer or terminal
and a modem or serial printer. Data is transmitted between the
devices via a cable with 25-pin, 9-pin, 8-pin or custom-built
connectors.
PIN ASSIGNMENTS
B-2
The entire standard covers many more functions than are used
in most data communications applications. Pin assignments are
factory set in the Courier to match the standard DB-25 assign-
ments in the following table. DB-9 connectors for AT-compatible
computers should be wired at the computer end of the cable as
shown in the DB-9 column. If you're using an Apple computer,
ask your dealer for the correct modem cable for your Apple
computer model.
Signal Flow
DB-25 DB-9 Circuit Function
DTE-DCE*
1
AA Chassis Ground both directions
2
3
BA Transmitted Data toDCE
3
2
BB Received Data to DTE
4
7 CA
Request to Send toDCE
5
8 CB Clear to Send to DTE
6
6
cc
Data Set Ready to DTE
7
5
AB Signal Ground both directions
8
CF Carrier Detect to DTE
12
SCF
Speed Indicate to DTE
15
DB
Synchronous Tx** Timing
to DTE
17
DD Synchronous Rx** Timing
to DTE
20 4
CD Data Terminal Ready toDCE
22
9
CE
Ring Indicate to DTE
24
DA Synchronous Tx** Timing
toDCE
*
DTE indicates the terminal or computer; DCE indicates the
modem.
**
Indicates Transmitter (TX) or Receiver (RX)
RS-232 Interface Pin Definitions
Summaries and Tables
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