Concept

Lookahead carry unit

Summary
A lookahead carry unit (LCU) is a logical unit in digital circuit design used to decrease calculation time in adder units and used in conjunction with carry look-ahead adders (CLAs). 4-bit adder A single 4-bit CLA is shown below: 16-bit adder By combining four 4-bit CLAs, a 16-bit adder can be created but additional logic is needed in the form of an LCU. The LCU accepts the group propagate (P_G) and group generate (G_G) from each of the four CLAs. P_G and G_G have the following expressions for each CLA adder: :P_G = P_0 \cdot P_1 \cdot P_2 \cdot P_3 :G_G = G_3 + G_2 \cdot P_3 + G_1 \cdot P_2 \cdot P_3 + G_0 \cdot P_1 \cdot P_2 \cdot P_3 The LCU then generates the carry input for each CLA. Assume that P_i is P_G and G_i is G_G from the ith CLA then the output carry bits are :C_{4} = G_0 + P_0 \cdot C_0 :C_{8} = G_
About this result
This page is automatically generated and may contain information that is not correct, complete, up-to-date, or relevant to your search query. The same applies to every other page on this website. Please make sure to verify the information with EPFL's official sources.
Related publications

Loading

Related people

Loading

Related units

Loading

Related concepts

Loading

Related courses

Loading

Related lectures

Loading