User`s guide

34 Di

ital Device Modelin

In the 74160 model, the boolean expressions are actually

reference functions. There are three reference functions

available: CHANGED, CHANGED_LH, and CHANGED_HL.

The format is:

function name (node, delta time)

For our example, we define the variable CLOCK as a logical

TRUE if there has been a LO-to-HI transition of the CLK signal

at simulation time. We define CNTENT as TRUE if there has

been any transition of the ENT signal at the simulation time.

Boolean operators take the following boolean values as

operands:

• reference functions

• transition functions

• previously assigned boolean variables

• boolean constants TRUE and FALSE

Transition functions have the general form of:

TRN_pn

For a complete list of reference functions and transition

functions, see the Digital Devices chapter in the online

MicroSim PSpice A/D Reference Manual.

PINDLY

PINDLY contains the actual delay and constraint expressions

for each of the outputs.

The CASE function defines a more complex, rule-based <delay

expression> and works as a rule section mechanism for

establishing path delays. Each boolean expression in the CASE

function is evaluated in order until one is encountered that

produces a TRUE result. Once a TRUE expression is found, the

delay expression portion of the rule is associated with the output

node being evaluated, and the remainder of the CASE function

is ignored. If none of the expressions evaluate to TRUE, then the

DEFAULT delay is used. Since it is possible for none of the

expressions to yield a TRUE result, you must include a default