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PSpice User Guide Digital simulation October 2019 606 Product Version 17.4-2019 © 1999-2019 All Rights Reserved. Strengths When a digital node is driven by more than one device, PSpice A/D determines the correct level of the node. Each output has a strength value, and PSpice A/D compares the strengths of the outputs driving the node. The strongest driver determines the resulting level of the node. If outputs of the same strength but different levels drive a node, the node's level becomes X. PSpice A/D supports 64 strengths. The lowest (weakest) strength is called Z. The highest (strongest) strength is called the forcing strength. The Z strength (called high impedance) is typically output by disabled tristate gates or open-collector output devices. PSpice A/D reports any nodes of Z strength (at any level) as Z, and reports all other nodes by the designations shown in Digital states on page 605. For additional information on this topic see Defining Output Strengths on page 396 of Chapter 7, "Digital device modeling."