2-4
Architecture
Lattice Semiconductor
LatticeXP Family Data Sheet
Table 2-1. Slice Signal Descriptions
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
Two additional signals: Carry Generate and Carry Propagate are generated per Slice in this mode, allowing 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.
Function
Type
Signal Names
Description
Input
Data signal
A0, B0, C0, D0 Inputs to LUT4
Input
Data signal
A1, B1, C1, D1 Inputs to LUT4
Input
Multi-purpose
M0
Multipurpose Input
Input
Multi-purpose
M1
Multipurpose Input
Input
Control signal
CE
Clock Enable
Input
Control signal
LSR
Local Set/Reset
Input
Control signal
CLK
System Clock
Input
Inter-PFU signal
FCIN
Fast Carry In
1
Output
Data signals
F0, F1
LUT4 output register bypass signals
Output
Data signals
Q0, Q1
Register Outputs
Output
Data signals
OFX0
Output of a LUT5 MUX
Output
Data signals
OFX1
Output of a LUT6, LUT7, LUT8
2 MUX depending on the slice
Output
Inter-PFU signal
FCO
For the right most PFU the fast carry chain output
1
2. Requires two PFUs.
Logic
Ripple
RAM
ROM
PFU Slice
LUT 4x2 or LUT 5x1
2-bit Arithmetic Unit
SP 16x2
ROM 16x1 x 2
PFF Slice
LUT 4x2 or LUT 5x1
2-bit Arithmetic Unit
N/A
ROM 16x1 x 2