Block Diagram for FIR Filter
Here is a mathematical model of Nth order FIR filter. "D" is a flip-flop , which means a delay element. N is "Tap Count" and able to be 4 to 380.

Block diagram of VHDL code is drawn like following. Data consists of DIOB bits(4 to 24) and is written into RAM. Coefficients consist of COB bits(4 to 32) and are read from ROM. We have only one DIOBxCOB multiplier and it accumulates its output to get filtered output, which consists of DIOB bits. Note: SRAM can be huge size and is not good for synthesis. You'd better use a hard macro cell or external SRAM.