Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!apple!portal!cup.portal.com!Radagast
From: Radagast@cup.portal.com (sullivan - segall)
Newsgroups: comp.sys.amiga
Subject: Re: Logic Simulator -- Need Parts Info
Message-ID: <34408@cup.portal.com>
Date: 30 Sep 90 22:16:51 GMT
References: <10804@hacgate.UUCP> <wayned.9608@wddami.spoami.com>
Distribution: na
Organization: The Portal System (TM)
Lines: 61

>>
>>I don't have that data book, but if it's not too difficult, I might try to
>>support some 74xx parts (no promises!).  How many *useful* ones are there?
>>Could someone please supply me with a basic parts list (please include the
>>part number, pins names, truth table/schematic)?
>>
>The 74xxx series of parts is probably the most prevalent series of
>integrated circuit logic functions available and the number of devices
>is _quite_ large (specially if you include the 74xx, 74LSxx, 74Sxx,
>74Fxx, 74HCxx, 74HCTxx, 74ACxx, 74ACTxx, 74HCTLSxx, etc families).
>Look in any of the TTL or CMOS logic family data books.

The types of things you will need to support for *generic* logic (including
the 74xx series) are:

     Propagation delays:
	Transition time Low to High
	Transition time High to Low
	Transition time Input(n) to Output(m)
	
     States:
        High, Low, Hi-Z, Open-Collector Output

     Clocks:
        Positive edge trigger
        Negative edge trigger
        High state
        Low state

     Timing:
        .5 ns (or less) to 1 second (or more)
        Crystal Oscillators
        Multiple nano-second delays
        

    Also, some circuits will not have a steady state representation.  Either
include warnings for these circuits, or simulate them down to the event
level (ie: Make transitions happen when they *should* and *in order*.

    I have source code in Turbo-C (my own) that implements some of these
features.  To avoid infinite loops I just evaluate the circuit for several
milliseconds while continuing to accept user input.  If there isn't a
steady state solution after that much time, the uncertain gates are left
in their last configuration.  

    To solve the problem for real, I would have had to maintain lists of 
events and their relative timing.  Then I could step from event to event
creating new events when the state of an output changes from a previous
event or from user input.  

                           -Sullivan_-_Segall (a.k.a. Radagast)
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