Issue link: https://resources.pcb.cadence.com/i/1180526
PSpice User Guide Digital device modeling October 2019 393 Product Version 17.4-2019 © 1999-2019 All Rights Reserved. Input/Output characteristics A digital device model's input/output characteristics are defined by the I/O model that it references. Some characteristics, such as output drive resistance and loading capacitances, apply to digital simulation. Others, such as the interface subcircuits and the power supplies, apply only to mixed analog/digital simulation. This section describes in detail: ■ the I/O model ■ the relationship between drive resistances and output strengths ■ charge storage on digital nets ■ the format of the interface subcircuits Input/Output model I/O models are common to entire logic families. For example, in the model libraries, there are only four I/O models for the entire 74LS family: IO_LS, for standard inputs and outputs; IO_LS_OC, for standard inputs and open-collector outputs; IO_LS_ST, for Schmitt trigger inputs and standard outputs; and IO_LS_OC_ST, for Schmitt trigger inputs and open-collector outputs. In contrast, timing models are unique to each device. I/O models are specified as .MODEL UIO [model parameters]* where valid model parameters are described in Table 7-2. INLD and OUTLD These are used in the calculation of loading capacitance, which factors into the propagation delay discussed under timing models on Timing model on page 387. Note that INLD does not apply to stimulus generators because they have no input nodes.