Shifting in / out

Hi.
I have a question aboutl Shifting.
As I have read you can use 3 digital pins (clock, data,latch) of an arduino to control an external bit shifter for adding more digital inputs or outputs
Also I read that you can control more than one external bit shifter with these pins.
But from examples I saw that always was for the same purpose.. Let's say that you had bitshifter for input and then Adding another input bitshifter also.

My question is :

Can you add both input and output bit shifter at the same time?
Can you use the same 3 pins for both different functions (input /output)

Thanks in advance

Ps : I wasn't sure if that was the right topic to post or to project guidance

I assume that you are talking about shift registers

Can you add both input and output bit shifter at the same time?

Yes

Can you use the same 3 pins for both different functions (input /output)

Yes, but it would not make sense.

What are you thinking of doing ?

For the kind of shift registers you are taking about, the kind that take 3 pins, for both input and output, you should use a fourth pin. MISO, MOSI, SCK & LATCH

caslor:
Let's say that you had bitshifter for input and then Adding another input bitshifter also.

What is the goal?

The type of shift resister that is normally used for an output expansion and the type used for an input expansion are two completely different chips.

In order to have a shift register that could cope with adding extra inputs or outputs they you would need one with a reset and clear on each bit ( flip flop) as well as an output. While you could build one of these any ready built chip would need three pins on the IC for each bit. Therefore an 8 bit shift register of this type would need 3 * 8 + Din + latch + power + ground = 28 pins.

The cost of a chip is highly dependent on the number of pins per package.

Better is the MCP23017 chip that gives you 16 bits each individual one can be set to be an input or output and has optional built in pull up resistors and signals out for bit changes. That takes the same 28 pin package and is a lot more bang for your buck.

As PaulRB says you will need 4 Arduino pins to drive this one as well.