The '595 is a nice device.

It's also pretty easy to use, but requires some understanding, as it is a tri-state registered-output serial-in, parallel-out shift register. If you want to assemble a byte from serial input, you have to clock the "srclk" input after each serial bit is presented at its serial data input. This increments the shift register into its next position. However, that is not sufficient to propagate the shift register output to the device output, as the shift register outputs are internal to the device and do not appear on any device pins.

After the 8th bit has been clocked into the shift register, the "rclk" must be clocked in order to transfer the internal shift register outputs to the register outputs. If this doesn't happen, the shift register outputs will not appear at the register outputs.

Since the device has tristate outputs, its output enable has to be driven in some way. In this case, it might be appropriate to tie it to GND, which always enables its outputs.

RE