Hello everyone! I'm fairly new to electronics and have been experimenting with an 74LS164 serial shift register (www.esi.uclm.es/www/isanchez/teco/ci/74164.pdf) and 8 leds (with resisters in series) on the register outputs (leds on when register output is low). I have this on a breadboard, and I'm using a computer power supply for the 5 volt power to the register and the leds. I would like to control the shift register using a parallel port and so I have tied register pin 2 (input B) to pin 14 on my parallel port (Autofeed line). Then I connected register pin 8 (clock pin) to pin 1 on the parallel port (strobe line). Register pin 1 (input A) and the master reset pin are tied high. The leds light up all right, but I thought this circuit would produce a shift on the register each time I set the strobe line from low to high, but instead it seems the register shifts continuously when the strobe line is low, and stops when it is high. Switching it quickly high-low-high (programtically) I get one to several shifts. So, have I misunderstood how the register works or perhaps the parallel port cant be used directly to the register clock pin? Do I need to add a capacitor(s) for this circuit to work properly? Any advice or wisdom on this matter would be greatly appreciated!