LFXP20E-4F256C Lattice, LFXP20E-4F256C Datasheet - Page 334

• 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
beginning of the design cycle. When the pipelining technique is applied, special care must be taken for the rest of
the design to account for the additional data path latency. The following illustrates the same data path before
(Figure 13-5) and after pipelining (Figure 13-6).
Figure 13-5. Before Pipelining
Figure 13-6. After Pipelining
Before pipelining, the clock speed is determined by the clock-to-out time of the source register, the logic delay
through four levels of combinatorial logic, the associated routing delays, and the setup time of the destination regis-
ter. After pipelining is applied, the clock speed is significantly improved by reducing the delay of four logic levels to
one logic level and the associated routing delays, even though the rest of the timing requirements remain the same.
It is recommended to check the Place and Route timing report to ensure that the pipelined design gives the desired
performance.
Comparing IF statement and CASE statement
CASE and IF-THEN-ELSE statements are common for sequential logic in HDL designs. The IF-THEN-ELSE state-
ment generally generates priority-encoded logic, whereas the CASE statement implements balanced logic. An IF-
THEN-ELSE statement can contain a set of different expressions while a Case statement is evaluated against a
common controlling expression. Both statements will give the same functional implementation if the decode condi-
tions are mutually exclusive, as shown in the following VHDL codes.
-- Case Statement — mutually exclusive conditions
process (s, x, y, z)
begin
end process;
O1 <= ‘0’;
O2 <= ‘0’;
O3 <= ‘0’;
case (s) is
end case;
FF1
when “00” => O1 <= x;
when “01” => O2 <= y;
when “10” => O3 <= z;
FF1
Function
Comb.
Function
Comb.
FF2
Slow Clock
Fast Clock
Function
Comb.
13-7
Function
Comb.
-- If-Then-Else — mutually exclusive conditions
process (s, x, y, z)
begin
end process;
O1 <= ‘0’;
O2 <= ‘0’;
O3 <= ‘0’;
if s = “00” then O1 <= x;
elsif s = “01” then O2 <= y;
elsif s = “10” then O3 <= z;
end if;
Function
Comb.
HDL Synthesis Coding Guidelines
for Lattice Semiconductor FPGAs
FF3
Function
FF1
Comb.
FF4