Every time you push a key, all bits stream are sent to the uC, so you really need to employ the brute force.
ex:
key1 MSB (39) 0......1 LSB(0)
key1 MSB (39) 0.....10 LSB(0)
and so on...

you need to define a initial condition. ex: all 0's
you enter
and your numbers, letters and special characters

if you are developping the keyboard you must take into account the hardware to produce the bits stream.

probably a buffer is needed to take every byte from it to the uC so you must use just one port for example P1.
flip flop can do this, a line control and a clock where you can control the clock as you want.

It is a hardware design consideration problem more that a firmware problem, i think!