PSpice User Guide

PSpice User Guide

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PSpice User Guide Digital device modeling October 2019 401 Product Version 17.4-2019 © 1999-2019 All Rights Reserved. It has four nodes as described. The AtoD subcircuit has one parameter, CAPACITANCE, which corresponds to the input load. PSpice passes the value of the I/O model parameter INLD to this parameter when the interface subcircuit is called. The DtoA interface subcircuit format is shown here: .SUBCKT DTOA + + + PARAMS: DRVL=<0 level driving resistance> + DRVH=<1 level driving resistance> + CAPACITANCE= + {N device, loading capacitor, and other + declarations} .ENDS It also has four nodes. Unlike the AtoD subcircuit, the DtoA subcircuit has three parameters. PSpice will pass the values of the I/O model parameters DRVL, DRVH, and OUTLD to the interface subcircuit's DRVL, DRVH, and CAPACITANCE parameters when it is called. The library file DIG_IO.LIB contains the I/O models and interface subcircuits for all logic families supported in the model libraries. You should refer to this file for examples of the I/O models, interface subcircuits, and the proper use of N and O devices. Shown below are the I/O model and AtoD interface subcircuit definition used by the primitives describing the 74393 part. .model IO_STD uio ( + drvh=96.4 drvl=104 + AtoD1="AtoD_STD" AtoD2="AtoD_STD_NX" + AtoD3="AtoD_STD" AtoD4="AtoD_STD_NX" + DtoA1="DtoA_STD" DtoA2="DtoA_STD" + DtoA3="DtoA_STD" DtoA4="DtoA_STD" + tswhl1=1.373 tswlh1=3.382ns + tswhl2=1.346ns tswlh2=3.424ns + tswhl3=1.511ns tswlh3=3.517ns + tswhl4=1.487ns tswlh4=3.564ns + ) .subckt AtoD_STD A D DPWR DGND + params: CAPACITANCE=0 * O0 A DGND DO74 DGTLNET=D IO_STD C1 A 0 {CAPACITANCE+0.1pF} .ends If an instance of the 74393 part is connected to an analog part via node AD_NODE, PSpice generates an interface block using the I/O model specified by the digital primitive actually at the interface. Suppose that U1 is the primitive connected at AD_NODE (see the

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