This is the input multiplexer select line to select between regular data input (DIN) or cascade data input (CASDIN) when the block RAM is in cascade mode. When the block RAM is not used in cascade mode, DIN is always selected.
This is the input multiplexer select line to select between regular data input (DIN) or cascade data input (CASDIN) when the block RAM is in cascade mode. When the block RAM is not used in cascade mode, DIN is always selected.