Keithley 2651A Reference Manual page 107

Model 2651A High Power System SourceMeter® Instrument Reference Manual
RS-232 connections
The RS-232 serial port is connected to the serial port of a computer using a straight-through RS-232
cable terminated with DB-9 connectors. Do not use a null modem cable. The serial port uses the
transmit (TXD), receive (RXD), CTS and RTS (if flow control is enabled), and signal ground (GND)
lines of the RS-232 standard.
See Flow control and signal handshaking
interface and the pinouts. The connector location is shown in
73).
If your computer uses a DB-25 connector for the RS-232 interface, you will need a standard cable or
adapter with a DB-25 connector on one end and a DB-9 connector on the other. An RS-232 cable is
available from the
The following table provides pinout identification for the 9-pin (DB-9) or 25-pin (DB-25) serial port
connector on the computer.
Computer serial port pinout
Signal*
DCD, data carrier detect
RXD, receive data
TXD, transmit data
DTR, data terminal ready
GND, signal ground
DSR, data set ready
RTS, request to send
CTS, clear to send
RI, ring indicator
* The Model 2651A does not use all RS-232 signals. See the topic
handshaking (on page 2-83).
2651A-901-01 Rev. A / March 2011
(on page 2-83) for the rear-panel connector for the RS-232
Keithley Instruments website
Communications interfaces
(http://www.keithley.com).
DB-9 pin number DB-25 pin number
1 8
2 3
3 2
4 20
5 7
6 6
7 4
8 5
9 22
Flow control and signal
Section 2: General operation
(on page 2-
2-85