Using an External Pull-Up
In general, an external pull-up is required only when you want to set the output “high” value greater than
TTL levels. For example, to use a +12V external power supply, the value of the external pull-up resistor is cal-
culated as follows:
V
cc
= 12 VDC
I
max
= I
out low
× safety factor = 1 mA × 0.5+0.5 mA
The value of the logic "high" level with the external 24 kΩ pull-up resistor is calculated as follows:
Driving External Switches
You can use two digital output channels to control an external switch. For example, you can drive the Key-
sight 876X series of microwave switches using an external power supply and two digital output channels.
The state of the 2-to-1 multiplexer is changed by setting the appropriate output bit low (0).
Keysight DAQ970A User's Guide 225
4Measurement Tutorials
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