If you JSR #$FFE4 (from assembly) the accumulator should return with the next character from the keyboard buffer.
If you load a character into the accumulator and JSR #$FFD2 the character should be output to the screen.
These ‘universal’ routines are part of the Kernal ROM jump table and ‘should’ be relatively stable across the different versions of BASIC, different keyboard models and (even) between the PET, VIC-20 etc.
If you can give us a little more information about what you are trying to achieve, then we way be able to advise you further.
Dave