On the '245 each I/O pin can be either an input or output. On the '244 each
pin is either an input or output.
I do not believe that the HC is specified as 5V tolerant inputs. Not sure.
If it isn't specified as such then you may have reliability issues later.
The AHC family does have 5V tolerant inputs and can be run with
a 3V supply. Also LCX, VHC, LVC have 5V tolerant inputs.
Some manufacturers have other logic family designators. Look
for "5V tolerant inputs"
The function of the buffer is to maintain signal integrity. Usually
buffers can drive high currents so more devices can be connected
to a data line.
(* jcl *)
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