http://www.allaboutcircuits.com/vol_4/chpt_12/4.html

We have chosen thehigh.HC594 serial-in/ parallel-out shift register with output register; though, it requires an extra pin, RCLK, to parallel load the shifted-in data to the output pins. This extra pin prevents the outputs from changing while data is shifting in. This is not much of a problem for LEDs. But, it would be a problem if driving relays, valves, motors, etc.

Code executed within the microprocessor would start with 8-bits of data to be output. One bit would be output on the "Serial data out" pin, driving SER of the remote 74AHC594. Next,
the microprocessor generates a low to high transition on "Shift clock", driving SRCLK of the '595 shift register. This positive clock shifts the data bit at SER from "D" to "Q" of the first shift register stage. This has no effect on the QA LED at this time because of the internal 8-bit output register between the shift register and the output pins (QA to QH). Finally, "Shift clock" is pulled back low by the microprocessor. This completes the shifting of one bit into
the '595.

I don't understand how this can shift anything with both RCLR and SRCLR inputs pulled high.

 

http://www.allaboutcircuits.com/vol_4/chpt_12/4.html



I don't understand how this can shift anything with both RCLR and SRCLR inputs pulled high.

Why? They are active-low clear inputs, pulling them high disables that function.