PS1='${PWD}' and make uppercase?

[Keith Ford x8614]

I noticed in a recent discussion that using PS1='${PWD}' will cause the
working directory path to become the UNIX prompt.  This works fine, but
is there a way to translate it to upper-case?  I've tried *many* times
using combinations of tr "[a-z]" "[A-Z]", but none have worked.  Chances
are this isn't possible and I just don't know UNIX, but hey, that's okay,
isn't it?  (:  TIA -kef
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