OR2C04A datasheet(9/192 Pages) ETC

9 / 192 page

Lucent Technologies Inc.

Data Sheet

June 1999

ORCA Series 2 FPGAs

Programmable Logic Cells (continued)

F5M and F5X Modes—Special Function Modes

The PFU contains logic to implement two special func-

tion modes which are variations on the F5 mode. As

with the F5 mode, the LUT implements two indepen-

dent five-input functions. Figure 6 and Figure 7 show

the schematics for F5M and F5X modes, respectively.

The F5X and F5M functions differ from the basic F5A/

F5B functions in that there are three logic gates which

have inputs from the two 5-input LUT outputs. In some

cases, this can be used for faster and/or wider logic

functions.

As can be seen, two of the three inputs into the NAND,

XOR, and MUX gates, F0 and F3, are from the LUT.

The third input is from the C0 input into PFU. Since the

C0 input bypasses the LUTs, it has a much smaller

delay through the PFU than for all other inputs into the

special PFU gates. This allows multiple PFUs to be

cascaded together while reducing the delay of the criti-

cal path through the PFUs. The output of the first spe-

cial function (either XOR or MUX) is F1. Since the XOR

and MUX share the F1 output, the F5X and F5M

modes are mutually exclusive. The output of the NAND

PFU gate is F2 and is always available in either mode.

To use either the F5M or F5X functions, the LUT must

be in the F5A/F5B mode; i.e., only 5-input LUTs

allowed. In both the F5X and F5M functions, the out-

puts of the five-input combinatorial functions, F0 and

F3, are also usable simultaneously with the special

PFU gate outputs.

The output of the MUX is:

F1 = (HLUTA & C0) + (HLUTB & C0)

F1 = (F3 & C0) + (F0 & C0)

The output of the exclusive OR is:

F1 = HLUTA

⊕ HLUTB ⊕ C0

F1 = F3

⊕ F0 ⊕ C0

The output of the NAND is:

F2 = HLUTA & HLUTB & C0

F2 = F3 & F0 & C0

5-2754(F).r3

Figure 6. F5M Mode—Multiplexed Function of Two

Independent Five-Input Variable

Functions

5-2755(F).r2

Figure 7. F5X Mode—Exclusive OR Function of Two

Independent Five-Input Variable

Functions

QLUT3

QLUT2

QLUT1

QLUT0

HLUTA

HLUTB

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