Referring to the figure on the left we see that externally it looks just like an ordinary 14-pin dual in-line chip. The extreme top left pin from the printed side is the first pin in the order, and the pin just opposite to it on the other row is the last or the 14th pin.
The following data gives its pin-out specifications:
Pin #14 is supply positive input,
Pin #7 is the negative or the ground pin of the IC,
Pin #8 is the clock input and receives externally applied oscillations,
Pin #9 is the reset input,
Pin-out 1 and 2 are the serial inputs of the IC.
The remaining pin-outs are all the outputs of the IC.
Basically in response to every clock input’s rising edge, the outputs serially produce one after the other a sequencing logic high at their pin-outs in the order 3-4-5-6-10-11-12-13 until all of them go high.
The serial inputs pin 1 and 2 of the IC has a special purpose of resetting the above procedure in an interesting pattern. For example if the pin – outs 1 and 2 are permanently connected to the positive supply and the reset pin is joined to the last output of the IC (pin #13), then, as discussed earlier, once all the outputs become high the last pin #13 instantly resets the whole circuit, shutting the whole array of outputs, and the cycle repeats.
Now suppose if through a simple wiring pins 1 and 2 are configured in such a way that when the last pin (#13) of the IC goes high while sequencing serially, it grounds the serial input (#1 and 2). The whole output array, instead of shutting down all together, now starts receding sequentially one-next-to-the-other, until all of them are shut down to begin the cycle all over again. This opposite sequencing also takes place in accordance to the rising pulse of the input clocks.
I hope it wasn’t all that difficult to understand the above functioning details of the IC 74LS164. Hopefully you will get to see another article pretty soon, which will explain the practical utility of this wonderful IC.