Appendix E
Interfacing to a Serial Device
© National Instruments Corp.
E-7 GPIB-232CT-A for MS-DOS/Windows
Custom Cables
If your application requires a custom cable, you can construct one if you
have a thorough knowledge of the handshaking protocols involved. Review
the RS -232 characteristics of your serial device and build the cable to
properly connect the handshake lines of the two devices. Because the
DTE-to -DCE connection is a straight across conne ction, it often involves
only connecting RTS to RTS, CTS to CTS, DTR to DTR, and so on. If the
documentation for your serial device does not provide a thorough
explanation of its handshaking protocol, the ANSI/EIA-232-C standard is a
good reference, provided your device conforms to the RS-232 protocol.
Caution: Although handshaking might not be required, it is best to use
some form of handshaking to prevent loss of data.
Interfacing the GPIB-232CT-A to a DTE with
Handshaking
For serial devices set up as DTEs, you must wire a DTE-to-DTE interface
cable, commonly known as a null modem cable. The cable allows the
GPIB-232CT-A to act as though it is communicating with a DCE, but it
swaps the appropriate pins to achieve a DTE configuration. This wiring
configuration is shown in Table E-3.
Table E-3. Cable Wiring Scheme for GPIB-232CT-A DTE to
Serial Device DTE
GPIB-232CT-A Signal to
DTE Serial Device Signal
Standard
DTE to DTE
9-pin 9-pin
Standard
DTE to DTE
9-pin 25-pin
RXD
to
TXD
2
to
3
2
to
2
TXD
to
RXD
3
to
2
3
to
3
DTR
to
DSR
4
to
6
4
to
6
GND
to
GND
5
to
5
5
to
7
RTS
to
CTS
7
to
8
7
to
5
CTS
to
RTS
8
to
7
8
to
4
Note : Connections in bold italics must be implemented.