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I'm experimenting with some 74hc595N shift registers and I think I'm missing something, I have my breadboard set up with the QH' output pin of the first register connected to the serial data pin of the second register, however this seems to make QH of the first register and QA of the second register behave the same, rather than in sequence.

My understanding is that when the SRCLK pin (I have my SRCLK and RCLK pins connected) goes from low to high, the contents of the shift register moves to the right. A high value in the QG position gets move into QH, and thus the QH' output pin also goes high. Since both registers share a clock, on the same pulse the high value on QH' gets read into the second register as it's QA value, thus the value of Reg1 QH and Reg2 QA will always change simultaneously to the same value

So I believe I understand why this is happening, but not how to prevent it since this seems to be the standard setup everyone recommends. Am I missing something?

quick and dirty wiring diagram of my setup (all outputs are connected to LEDs):

quick and dirty wiring diagram of my setup

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Try feeding IC1's QH into IC2's SER.

enter image description here

That way when CLOCK goes high you're reading the value of QH from the previous cycle. That's the way QG is passed to QH internally (he says without checking).

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  • \$\begingroup\$ Correct, QH' is the output of the last bit of the shift register before it goes into the output latch. \$\endgroup\$ – Finbarr May 18 '20 at 5:46

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