LFXP20E-4F256C Lattice, LFXP20E-4F256C Datasheet - Page 337

• Manufacturer Part Number: LFXP20E-4F256C
• Description: IC FPGA 19.7KLUTS 188I/O 256-BGA
• Manufacturer: Lattice

Specifications of LFXP20E-4F256C

• Lead Free Status / Rohs Status: Contains lead / RoHS non-compliant

Lattice Semiconductor
Implementing Multiplexers
The flexible configurations of LUTs can realize any 4-, 5-, or 6-input logic function like 2-to-1, 3-to-1 or 4-to-1 multi-
plexers. Larger multiplexers can be efficiently created by programming multiple 4-input LUTs. Synthesis tools camn
automatically infer Lattice FPGA optimized multiplexer library elements based on the behavioral description in the
HDL source code. This provides the flexibility to the Mapper and Place and Route tools to configure the LUT mode
and connections in the most optimum fashion.
Clock Dividers
There are two ways to implement clock dividers in Lattice Semiconductor FPGA devices. The first is to cascade the
registers with asynchronous clocks. The register output feeds the clock pin of the next register (Figure 13-7). Since
the clock number in each PFU is limited to two, any clock divider with more than two bits will require multiple PFU
implementations. As a result, the asynchronous daisy chaining implementation of clock divider will be slower due to
the inter-PFU routing delays. This kind of delays is usually ambiguous and inconsistent because of the nature of
FPGA routing structures.
Figure 13-7. Daisy Chaining of Flip-flops
16:1 MUX
…
process(sel, din)
…
LU
D
begin
end process;
if
elsif (sel="0001") then muxout <= din(1);
elsif (sel="0010") then muxout <= din(2);
elsif (sel="0011") then muxout <= din(3);
elsif (sel="0100") then muxout <= din(4);
elsif (sel="0101") then muxout <= din(5);
elsif (sel="0110") then muxout <= din(6);
elsif (sel="0111") then muxout <= din(7);
elsif (sel="1000") then muxout <= din(8);
elsif (sel="1001") then muxout <= din(9);
elsif (sel="1010") then muxout <= din(10);
elsif (sel="1011") then muxout <= din(11);
elsif (sel="1100") then muxout <= din(12);
elsif (sel="1101") then muxout <= din(13);
elsif (sel="1110") then muxout <= din(14);
elsif (sel="1111") then muxout <= din(15);
else muxout <= '0';
end if;
PFU
(sel="0000") then muxout <= din(0);
13-10
LU
D
PFU
HDL Synthesis Coding Guidelines
for Lattice Semiconductor FPGAs