Architecture
LatticeECP/EC Family Data Sheet
Lattice Semiconductor
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
Ripple
RAM
SPR16x2
N/A
ROM
PFU Slice
PFF Slice
LUT 4x2 or LUT 5x1
LUT 4x2 or LUT 5x1
2-bit Arithmetic Unit
2-bit Arithmetic Unit
ROM16x1 x 2
ROM16x1 x 2
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
SPR16x2
DPR16x2
Number of slices
1
2
Note: SPR = Single Port RAM, DPR = Dual Port RAM
2-5
LATTICE [ LATTICE SEMICONDUCTOR ]
