3: Functions and features Model 2450 Interactive SourceMeter® Instrument
3-64 2450-901-01 Rev. B/September 2013
Digital I/O lines
You can place each digital I/O line one of three modes: input, output, or open-drain.
When you configure the digital I/O, configure the output line before the input line. This prevents false
input trigger detection.
When you place a line in output mode, you can set the line as logic high (+5 V) or as logic low (0 V).
The default level when the line is set to output is logic low (0 V). When you read the line while it is in
this mode, it shows the present output status. It will not show external events.
When you place a line in input mode, each line is pulled up to +5 V while it detects external events.
You cannot toggle the logic level while the line is in input mode. If you attempt to toggle the logic
level, a warning message is generated.
When you place a line in open-drain mode, the line is configured to be an open-drain signal. This
makes the line compatible with other instruments that use open-drain digital I/O lines, such as legacy
Keithley Instruments products. You must write a 1 to any digital I/O line that is used as an input while
in open-drain mode.
Each digital I/O line can be used for digital control or as a trigger line. You can control the line using
either instrument commands or the trigger model. You can also configure the line for synchronous
triggering using one of two synchronous modes. See Understanding synchronous triggering modes
(on page 3-92) for more information.
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