This one, perhaps:
Yes, that's the Typo patent. Notice that it features "method and
apparatus". The bizarre idea of doing it in hardware was a figment of
the patent department's imagination. This was a dance to circumvent
the belief at the time that software could not be patented. Software
was smuggled in by stating that it was one way to realize the
apparatus in the patent disclosure.
The now obsolete belief was fallout from Gottsschalk v Benson, in
which the Supreme Court invalidated another Bell Labs patent, on a
trick to save a few cycles in converting integers between BCD and
binary. The grounds for rejection were roughly that software was math
(a "mental step") and therefore not patentable.
The Benson decision, written by William O. Douglas, makes ludicrous
reading: it argues, though the patent does not claim, that a patent on
this narrow method could be enforced against any program that converts
BCD to binary. Apparently Douglas thought that all black-box programs
for a given purpose were the same, although the patent office did not
so conflate different mechanical or electrical apparatuses that have a
common purpose.
Doug