Foggy on Shift Registers

Thread Starter


Joined Apr 25, 2009
Hi I recently purchased some serial in parallel out 3 stage shift registers (part num 74HC595). I have gotten interesting random results with some simple programing of my arduino (my microcontroller) but the actual function of the three pins data, SH, and ST still elude me.
I have researched the web including this site.
Do I have it right:
Data Pin (pin14): This pin decides the state of each register/bit (high or low)
SH_Clock(pin12): This is the clock that simply reads the data pin state every pulse
ST_Clock(pin11): Called latch pin, when this goes high all the bits collected and pushed out, creating the parallel effect. This pin is what collects the byte and moves it.

Is this basically correct?

Thanks again,
PS these chips are being used as demultiplexers
Last edited:


Joined Jul 17, 2007
Take a look at Texas Instruments' datasheet for the SN74HC595:

There's a function table on page 2, logic diagram on page 3, and timing diagram on page 4.

Pin 14 is the serial data input.
Pin 12 latches the data in the shift register to the output when it transitions from low to high.
Pin 11, when transitioned from low to high, shifts everything one bit to the right and copies the data present at the serial data input into the 1st shift register.