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