LFEC10 datasheet(8/163 Pages) LATTICE

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2-5

Architecture

Lattice Semiconductor

LatticeECP/EC Family Data Sheet

Modes of Operation

Each Slice is capable of four modes of operation: Logic, Ripple, RAM and ROM. The Slice in the PFF is capable of

all modes except RAM. Table 2-2 lists the modes and the capability of the Slice blocks.

Table 2-2. Slice Modes

Logic Mode: In this mode, the LUTs in each Slice are conﬁgured as 4-input combinatorial lookup tables. A LUT4

can have 16 possible input combinations. Any logic function with four inputs can be generated by programming this

lookup table. Since there are two LUT4s per Slice, a LUT5 can be constructed within one Slice. Larger lookup

tables such as LUT6, LUT7 and LUT8 can be constructed by concatenating other Slices.

Ripple Mode: Ripple mode allows the efﬁcient implementation of small arithmetic functions. In ripple mode, the fol-

lowing functions can be implemented by each Slice:

• Addition 2-bit

• Subtraction 2-bit

• Add/Subtract 2-bit using dynamic control

• Up counter 2-bit

• Down counter 2-bit

• Ripple mode multiplier building block

• Comparator functions of A and B inputs

- A greater-than-or-equal-to B

- A not-equal-to B

- A less-than-or-equal-to B

Ripple Mode includes an optional conﬁguration that performs arithmetic using fast carry chain methods. In this

conﬁguration (also referred to as CCU2 mode) two additional signals, Carry Generate and Carry Propagate, are

generated on a per slice basis to allow fast arithmetic functions to be constructed by concatenating Slices.

RAM Mode: In this mode, distributed RAM can be constructed using each LUT block as a 16x1-bit memory.

Through the combination of LUTs and Slices, a variety of different memories can be constructed.

The Lattice design tools support the creation of a variety of different size memories. Where appropriate, the soft-

ware will construct these using distributed memory primitives that represent the capabilities of the PFU. Table 2-3

shows the number of Slices required to implement different distributed RAM primitives. Figure 2-5 shows the dis-

tributed memory primitive block diagrams. Dual port memories involve the pairing of two Slices, one Slice functions

as the read-write port. The other companion Slice supports the read-only port. For more information about using

RAM in LatticeECP/EC devices, please see the list of technical documentation at the end of this data sheet.

Table 2-3. Number of Slices Required For Implementing Distributed RAM

Logic

Ripple

RAM

ROM

PFU Slice

LUT 4x2 or LUT 5x1

2-bit Arithmetic Unit

SPR16x2

ROM16x1 x 2

PFF Slice

LUT 4x2 or LUT 5x1

2-bit Arithmetic Unit

N/A

ROM16x1 x 2

SPR16x2

DPR16x2

Number of slices

Note: SPR = Single Port RAM, DPR = Dual Port RAM

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