My homework is to build a 16 bit adder with "4 bit carry look-ahead". I know how to build a simple 16 bit adder but how do i implement the "4 bit carry look-ahead". In addition i also have to make it expandable so that i can make a ALU which has a subtractor , multiplier and divider (which i'll worry about later). So for the mean time can somebody please tell me how to implement a "4-bit carry look ahead" on a 16 bit adder? (has to be done on a software called tanner).

Thanks in advance!

 

I don't know if this will help, but check out this link:
http://www.writphotec.com/mano4/Supplements/Carrylookahead_supp4.pdf

 

I don't know what a 4-bit carry lookahead is. I would look into the 'simple processor', which accepts commands in their registers to perform various functions in the ALU.

Is this a parallel input? Or, is it a machine? (sync , or async)

Is the 16-bit adder one with 16-bit inputs, or outputs?

Can you use the logic outputs of the adder (the sum) to create the carry look-aheads with some logic?

Steve

 

Get the data sheet for a 74LS182. It's a lookahead carry generator.

 

Here's a hint: Get the datasheet for the CD4008 4 bit full adder with look-ahead carry and duplicate the functionality.

 

A [*edit* simple] lookahead carry is just ANDing the two previous bits of the operands together.