3 Input Adder in Stratix II Using 1 ALM

Question

There is a great link on the Altera web page explaining how to implement a 3 input parallel adder in one ALM.

I used the "Parallel Add" function in the MegaWizard to try and implement this for a Stratix II GX target.

Unfortunately, it uses 2 ALMs.

Does anybody know if there is a special QII setting or coding style that must be used to get the 1 ALM implementation?

Thanks.

altera_forum · Answer

I just use assign "sum = a+b+c" in Verilog.

You need to be a little careful with the grouping in adder trees, matching up the bitwidths, etc. There is some discussion in this manual -

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