Keithley 2651A Reference Manual page 191

Section 3: Functions and features
Connecting cables
Use a cable equipped with a male DB-25 connector (Keithley Instruments part number CA-126-1), or
a Model 2600-TLINK cable to connect the digital I/O port to other Keithley Instruments models
equipped with a Trigger Link (TLINK).
Digital I/O lines
The port provides 14 digital I/O lines. Each output is set high (+5 V) or low (0 V) and can read high or
low logic levels. Each digital I/O line is an open-drain signal.
+5 V output
The digital I/O port provides a +5 V output that is used to drive external logic circuitry. Maximum
current output for this line is 250 mA. This line is protected by a self-resetting fuse (one hour recovery
time).
Output enable line
The Model 2651A output enable (OE) line of the digital I/O can be used with a switch in the test fixture
or component handler. With proper use, power is removed from the DUT when the lid of the fixture is
opened. See
The digital I/O port of the Model 2651A is not suitable for control of safety circuits and should
not be used to control a safety interlock. When an interlock is required for safety, a separate
circuit should be provided that meets the requirements of the application to reliably protect
the operator from exposed voltages.
Digital I/O configuration
The following figure shows the basic configuration of the digital I/O port. Writing a 1 to a line sets that
line high (~ +5 V). Writing a 0 to a line sets that line low (~0 V). Note that an external device pulls an
I/O line low by shorting it to ground, so that a device must be able to sink at least 480 μA per I/O line.
3-84
Model 2651A High Power System SourceMeter® Instrument Reference Manual
Using output enable (on page 3-88) for more details.
WARNING
2651A-901-01 Rev. A / March 2011