Table Of Contents

Digital Logic States

Last Modified: April 19, 2018

Test engineers can choose from a number of different digital I/O instruments with a range of features for communication and test applications. Beyond the basic capabilities of driving a digital pattern of 1s and 0s, digital instruments often support waveforms that can include some or all of the logic states shown in the following table.

Logic State Drive Data Expected Response
Drive States 0 Logic Low Don't Care
1 Logic High Don't Care
Z Disable Don't Care
Compare States L Disable Logic Low
H Disable Logic High
X Disable Don't Care

The six logic states control the voltage driver and, if supported, the compare engine of the digital tester (such as a DAQ device) on a per clock cycle basis. Drive states specify what stimulus data the digital tester drives on a particular channel or when to disable the voltage driver (referred to as the tristate or high-impedence state). Compare states indicate the expected response from the device under test. These six logic states make it possible to perform bidirectional communication and real-time hardware comparison of acquired response data.

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