1.1 Logic Element

The logic element consists of a 4-input Lookup Table (LUT) with a carry chain and D-type flip-flop, as shown in Figure   1. The logic element is fracturable, which means that the LUT can be independently used without flip-flop, or flip-flop can be used without LUT.

The 4-input LUT with carry chain can be configured to implement any 4-input combinational logical function or arithmetic function. The 4-input LUT generates the output (Y) depending on the four inputs—A, B, C, and D. The carry chain is implemented using a 3-bit carry-look-ahead circuit. This circuit is connected between various logic elements by carry chain input (Cin) signal and carry chain output (Cout) signal. When the LUT is used to implement arithmetic functions, the carry chain input (Cin) is used with LUT output to generate the Sum (S) output. However, for non-arithmetic functions, the sum (S) output can still be used as an output along with the other output (Y).

The D-type flip-flop can be used as a register or latch. The data input (D) of the D-type flip-flop can be sourced from one of three inputs: the direct input (D1), the combinational output (Y) of the LUT, or the sum output (S) of the LUT (Figure   1). The ALn and SLn are asynchronous load and synchronous load active-low signals that can be configured as reset signal. The flip-flop output (Q) can be an output of the logic element or one of the data inputs to the 4-input LUT (inside the same logic element).