Section 8: Triggering
2470 High Voltage SourceMeter Instrument Reference Manual
8-16
2470-901-01 Rev. A /
May
2019
+5 V line
The digital I/O port provides a +5 V output. You can use this line to drive external circuitry. The
maximum current output for this line is 500 mA. A self-resetting fuse with a one-hour recovery time
protects this line.
If you are using this supply to drive a relay, it should be connected to the V
ext
line so that the relay is
protected by the flyback diode clamp.
Digital I/O lines
You can place each digital I/O line into one of the following modes:
•
Digital open-drain, output, or input
•
Trigger open-drain, output, or input
•
Trigger synchronous master or acceptor
When you configure the digital I/O lines for triggering applications, configure the output lines before
the input lines. This prevents possible false input trigger detection in certain situations.
Digital control modes
If you are setting a line for digital control, you can set the line to be open-drain, output, or input, as
described in the following topics.
Open-drain
When you place a line in open-drain mode, the line is configured to be an open-drain signal with a
100 k
Ω
pull-up resistor. This makes the line compatible with other instruments that use open-drain
digital I/O lines, such as other Keithley Instruments products that only support open-drain for its digital
I/O. In this mode, the line can serve as an input, an output, or both. You can read from the line or
write to it. When a digital I/O line is used as an input in open-drain mode, you must write a
1
to the
line to enable it to detect logic levels that are generated from external sources.
Output
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 is logic low (0 V). When the instrument is in output mode, the line is actively driven
high or low. Unlike the input or open-drain modes, it will not respond to externally generated logic
levels.
When you read the line, it shows the present output status and an event message is generated.
