Hi,

I've got a project that requires the use of a 74165 shift register. However, after countless hours of testing and re-connecting of wires, I don't seem to get it working.

Basically I want, for test purposes, to load 1010 from the parallel input pins and shift it out serially. I have tested it using multisim and sometimes it works but now it does not work watsoever. I've also tried it practically by buying the IC and trying to get the same results, but no luck.

I have attach a schematic that use to work ONLY on multisim.

Thank you

 

I do not know what you mean by "it does not work", if that is, that you do not get what you expect out of the register, then what I would try to do is to keep the "clock inhibit" input high until you are ready to shift your data out of the register. According to the Function Table, when you go from load to shift, the data from parallel input "H" is on the output Q and on the next positive edge of the clock, the data from "G" is on the output Q and "A" will be the last bit out seven clock cycles later. Hope this helps out.
Retiredguy

 

I'll agree, it's probably a timing issue somewhere although these type ICs are usually pretty forgiving.

http://focus.ti.com/lit/ds/symlink/cd74hct165.pdf

 

The OP still needs to hold the parallel load high for a minimum of 8 clock cycles.