Parallel 4 bit adder

Thread Starter

Tom Parry

Joined Feb 27, 2018
Below is the parallel adder circuit using d flip flops as shift registers , my lecturer is useless and his answer is we dont need to see it working . Which doesn't help any situation really
i have no idea why all the probes are on , output is the same when reset loaded etc
any help appreciated



Joined Mar 30, 2015
Welcome to AAC!

Edited image:
What is the circuit supposed to do?

What type of components are U18, U17, ...? Why do you have all of them controlled by the same key?

Thread Starter

Tom Parry

Joined Feb 27, 2018
Basically is a 4 bit adder which takes parallel inputs and outputs serial,
top register loads in on clock to b register ,
b register clocked into adder by clock
and the process is done again too add two 4 bit values

u 18 is active high right now as spec to reset on active low u17 is a basically a clock input but used here as interactive to make life easier

basically we were told to create a 4 bit adder nothing about serial or parallel mentioned at all, and we were given pretty much this schematic without any outputs


Joined Mar 31, 2012
What is it that this schematic you were given supposed to do, as given to you? Is it supposed to be something close to what you are supposed to come up with and you need to tweak it? Is it just a schematic with a bunch of parts that you might need? What?

If you were just told to create a 4-bit adder without any qualifiers, then why not just create a vanilla 4-bit adder that takes two 4-bit unsigned integers and outputs the 5-bit result?

The question still stands about why all of these inputs seem to be keyed to the same input, namely the space bar?

Thread Starter

Tom Parry

Joined Feb 27, 2018
Honestly ignore the space bar part i can change each one separable by the click of the mouse??

Its a 4 bit parallel to serial adder and does what it says on the tin

it pretty much adds two numbers inserted parallel and outputs in serial once added together

the schematic as it should be, but it doesn't do as it should