[sdiy] moog module designs

[Scott Gravenhorst]

>Neil Johnson <neil.johnson97 at ntlworld.com> wrote:
>>Hi,
>>
>>Scott Gravenhorst wrote:
>>> Thank you, Tim.  I guess it's something to be aware of.  I went to 
>>> their
>>> site and tried to look up 4027, but it doesn't seem to be there.
>>
>>The HCF4027 is on the ST website:
>>
>>	http://www.st.com/stonline/books/ascii/docs/2039.htm
>>
>>> Interesting that they didn't have the "J and K high" condition in their
>>> truth table.
>>
>>In a way they do --- the 'X' refers to "don't care"... so the lines
>>
>>J	K	Q 	-> 	Q	Q'
>>H	X	L		H	L
>>X	H	H		L	H
>>
>>say exactly what happens for J = K = high, i.e., it toggles.

Looking at this again, I disagree that this truth table correctly shows
what happens with J and K both high.  if X means "don't care", then the
table is ambiguous.  i.e., for J=H and K=X, what of X is high? then J=H,
K=H and Q=H.  Now look at J=X and K=H.  If X is H, then J=H and K=H and
then Q is LOW?  That conflicts with the first statement.

So this does not represent toggle, it represents an ambiguous logic
function and is without meaning.

That's not a truth table, it's a lie table.  

Other mfrs do not use X in that part of the truth table.  X appears only in
the part dealing with direct set and direct reset in which cases both J and
K are assigned X for don't care.

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