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Analog and Significant Event Digital Simulator

IP.com Disclosure Number: IPCOM000045858D
Original Publication Date: 1983-Apr-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 4 page(s) / 29K

Publishing Venue

IBM

Related People

Bach, WS: AUTHOR [+2]

Abstract

An existing significant event simulator for design verification of digital logic and other digital circuits is used with modifications patterned after the existing simulator to also report the response of analog circcuits. The simulator is forced to examine the analog circuits at regular intervals, while the digital circuits continue to be examined only at significant events. Reporting conventions which have identical or analogous meaning for analog circuits are retained. For example, the symbol "1" is used to report logic 1 for digital and to report voltage rise for analog. The symbol "H" reports high impedance for digital, which occurs when all drivers are down. No analogous condition to drivers being up or down exists for analog, and the "H" is used to report certain conditions peculiar to analog circuits.

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Analog and Significant Event Digital Simulator

An existing significant event simulator for design verification of digital logic and other digital circuits is used with modifications patterned after the existing simulator to also report the response of analog circcuits. The simulator is forced to examine the analog circuits at regular intervals, while the digital circuits continue to be examined only at significant events. Reporting conventions which have identical or analogous meaning for analog circuits are retained. For example, the symbol "1" is used to report logic 1 for digital and to report voltage rise for analog. The symbol "H" reports high impedance for digital, which occurs when all drivers are down. No analogous condition to drivers being up or down exists for analog, and the "H" is used to report certain conditions peculiar to analog circuits.

The existing simulator for digital circuits is implemented as a program. That program is designed to report only changes when significant changes occur. To avoid major modification of that program, a rising analog signal is reported as 1 H 1 H 1 H, each report symbol representing the condition at one of the intervals at which the analog circuit is examined. Similarly, a falling is reported as 0 H 0 H 0
H. The symbol "H" is also reported when a voltage change is observed at the next time following the report of an unknown voltage or an uninitialized voltage.

The following table details the reporting symbols and the meaning of each for a digital circuit and an analog circuit. Meaning

Reporting Digital Analog

Symbol Circuit Circuit 1 Logic 1 Rise in voltage

No change since No change since

last rise and no last rise reported

significant event as 1

0 Logic 0 Fall in voltage

- No change since No change since

last fall and no last fall reported

significant event as 0

x Unknown logic Unknown voltage

= No change in unknown No change in unknown

logic and no voltage

significant event

U Uninitialized logic Uninitialized voltage

H High impedance Rise if after 1 or +

(Drivers down) Fall if after 0 or -

Change if after X,U or =

$ No change from high No change in known

impedance and no voltage reported as H

significant event.

The following timing chart shows an intermediate part of a typical report, simplified in that it shows only a few time periods and reports for only one analog circuit and two digital circuits.

This printed chart constitutes the end product of the simulator, and

1

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is readily and usefully interpreted by circuit designers having knowledge of the meaning of the reporting symbols. In practice, of course, the report would be for an extended period and for hundreds or even thousands of circuits. In the following chart, the analog circuit is examined each 100 time intervals. TIMING CHART

Time Intervals Analog Cir Digital Cir 1 Digital Cir 2 500 1 $ $

525 H 1 $

550 1 + 0

600 + + -

610 + 0 -

675 + -1

700 H - +

720 $ x +

800 0 = U

900 H = 1

925 0 H +

1000 x $ +

1100 H $ +....