
Data Sheet
June 1999
ORCA Series 2 FPGAs
6
Lucent Technologies Inc.
Programmable Logic Cells 
(continued))
Key: C = controlled by configuration RAM.
Figure 3. Simplified PFU Diagram
5-4573(F)
A4
A3
A2
A1
A4
A3
A2
A1
QLUT3
A0
CARRY
CARRY
A3
A2
A1
A0
QLUT2
B4
B3
B2
B1
B4
B3
B2
B1
QLUT1
B0
CARRY
CARRY
B3
B2
B1
B0
QLUT0
CIN
C0
LSR
GSR
WD[3:0]
CK
CKEN
TRI
PFU_XOR
B4
A4
PFU_NAND
PFU_MUX
C
C
C
C
WD3
WD2
WD1
WD0
C
C
C
T
T
T
T
REG3
SR
EN
REG2
SR
EN
REG1
SR
EN
REG0
SR
EN
O4
O3
O2
O1
O0
F3
C
C
COUT
F2
F1
F0
D0
D1
D2
D3
Q0
Q1
Q2
Q3
C
T
T
T
T
C
Figure 2 and Figure 3 show high-level and detailed 
views of the ports in the PFU, respectively. The ports 
are referenced with a two- to four-character suffix to a 
PFU’s location. As mentioned, there are two 5-bit input 
data buses (A[4:0] and B[4:0]) to the LUT, one 4-bit 
input data bus (WD[3:0]) to the latches/FFs, and an 
output data bus (O[4:0]).
Figure 3 shows the four latches/FFs (REG[3:0]) and the 
64-bit look-up table (QLUT[3:0]) in the PFU. The PFU 
does combinatorial logic in the LUT and sequential 
logic in the latches/FFs. The LUT is static random 
access memory (SRAM) and can be used for read/
write or read-only memory. The eight 3-state buffers 
found in each PLC are also shown, although they actu-
ally reside external to the PFU.
Each latch/FF can accept data from the LUT. Alterna-
tively, the latches/FFs can accept direct data from 
WD[3:0], eliminating the LUT delay if no combinatorial 
function is needed. The LUT outputs can bypass the 
latches/FFs, which reduces the delay out of the PFU. It 
is possible to use the LUT and latches/FFs more or 
less independently. For example, the latches/FFs can 
be used as a 4-bit shift register, and the LUT can be 
used to detect when a register has a particular pattern 
in it.