Hi,
I included the DC Source DC1 to set a minimum level for when the two binary inputs are both off. Use a DC Source anywhere a constant numerical value is needed.
The DC Source block lets you choose both the numeric value of your constant and its format -- how many binary bits appear before and after the decimal point (actually the correct term here would be "binary point."). See http://ez.analog.com/docs/DOC-3168
for help with the number formats in SigmaDSP.
Bob