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AR# 21511

LogiCORE Multiplier Accumulator (MACC) v4.0 - Why does the MAC FIR fail to generate if I set the number of cycles to larger than 4095 for my 18x18 MAC when targeting Virtex-4, even though the GUI says the MAX range is 16384?

Description

Why does the MAC FIR fail to generate if I set the number of cycles to larger than 4095 for my 18x18 MAC when targeting Virtex-4, even though the GUI says the MAX range is 16384?

Solution

This limit is only for Virtex-4, and is because the Multiplier Accumulator (MACC) cannot use more than 1 DSP48 and the bit growth can be only 12 bits. This limits the maximum number of cycles to 4095 when the inputs are 18x18.

AR# 21511
Date Created 09/04/2007
Last Updated 05/19/2014
Status Archive
Type General Article