PSpice User Guide

PSpice User Guide

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PSpice User Guide Digital device modeling October 2019 402 Product Version 17.4-2019 © 1999-2019 All Rights Reserved. 74393 subcircuit definition on page 385), and that the IO_LEVEL is set to 1. PSpice determines that IO_STD is the I/O model used by U1. Notice how IO_STD identifies the interface subcircuit names AtoD_STD and DtoA_STD to be used for level 1 subcircuit selection. If the connection with U1 is an input (such as a clock line), PSpice creates an instance of the subcircuit AtoD_STD: X$AD_NODE_AtoD1 AD_NODE AD_NODE$AtoD $G_DPWR + $G_DGND + AtoD_STD + PARAMS: CAPACITANCE=0 The AtoD_STD interface subcircuit references the DO74 model in its PSpice O device declaration. This model, stated elsewhere in the model libraries, describes how to translate an analog signal on the analog side of an interface node, to a digital state on the digital side of an interface node. .model DO74 doutput + s0name="X" s0vlo=0.8 s0vhi=2.0 + s1name="0" s1vlo=-1.5 s1vhi=0.8 + s2name="R" s2vlo=0.8 s2vhi=1.4 + s3name="R" s3vlo=1.3 s3vhi=2.0 + s4name="X" s4vlo=0.8 s4vhi=2.0 + s5name="1" s5vlo=2.0 s5vhi=7.0 + s6name="F" s6vlo=1.3 s6vhi=2.0 + s7name="F" s7vlo=0.8 s7vhi=1.4 + The DOUTPUT model parameters are described under O devices in the online PSpice Reference Guide. Supposing the output of the 74393 is connected to an analog part via the digital primitive UBUFF. At IO_LEVEL set to 1, PSpice determines that the DtoA_STD interface subcircuit identified in the IO_STD model, should be used. .subckt DtoA_STD D A DPWR DGND + params: DRVL=0 DRVH=0 CAPACITANCE=0 * N1 A DGND DPWR DIN74 DGTLNET=D IO_STD C1 A DGND {CAPACITANCE+0.1pF} .ends For this subcircuit, the DRVH and DRVL parameters values specified in the IO_STD model would be passed to it. (The interface subcircuits in the model libraries do not currently use these values.) The DtoA_STD interface subcircuit references the DIN74 model in its PSpice N device declaration. This model, stated elsewhere in the libraries, describes how to translate a digital state into a voltage and impedance.

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