Re: Greg's questions

[Greg Alexander <galexand@xxxxxxx>]

>The first 8 MuP21 chips were prototyed in ceramic packages.
>The production P21 was done in plastic.  The plastic package
>intoduced a problem that was not present on the ceramic
>packages possibly due to increased inductance on the lead
>wires.  The bottom line was that A! became marginal.
>
>Not all instructions take the same amount of current.  Some
>required more power than others.  A! is one of those.  With
>the introduction of the plastic package some code that had
>worked on ceramic packages broke.  It turned out that the
>cause was A! failing.  It worked better in some slots than
>in others.  The conservative fix was to preceed A! with a
>NOP. It might or might not be needed in each case but it
>provided a simple work around for the package introduced
>problem.  I understand that the problem is not present
>on the plcc package. (shorter lead wires)

Do you mind if I include this description in the FAQ?  I think it is a
good explanation of the issues surrounding the plastic vs. ceramic, and
A!.  I don't really expect an answer, but it would be nice: is this the
same restriction Ting is referring to with the text "If T register was
changed in the previosu instructian, and A! is not in slot0, a nop is
needed before A! to let T stabilize."  I ask because I want to know in
what situations we can remove the NOP.
	Thanks.