Examples of FPLD Families:
Actel ACT,
Xilinx LCA,
Altera MAX 5000 & 7000
1
Actel ACT Family
¯ The Actel ACT family employs multiplexer-based logic cells.
¯ A row-based architecture is used in which the logic cells are arranged in rows with
horizontal routing channels between adjacent rows of logic cells.
Interconnect
Logic cell
2
ACT 1 Logic Modules
¯ ACT 1 FPGAs use a single type of logic module.
Logic Module
Actel ACT
M1
A0
A1
0
1
S
0
1
S
B1
SB
SA
F
D
F1
'1'
F2
C
B0
B1
F2
D
'1'
SB
S3
S0
S1
F
A1
M3
M2
B0
Logic Module
A0
F1
0
1
S
SA
(a)
Logic Module
S0
F1
0
1
0
1
F
F2
A
S3
S1
O1
0
1
'0'
B
O1
F = (A · B) + (B' · C) + D
(b)
(c)
(d)
(a) An Actel FPGA. (b) An ACT 1 logic module. (c) An implementation of an ACT 1 logic module using
pass transistors. (d) An example of function implementation by an ACT 1 logic module.
3
ACT 2 and ACT 3 Logic Modules
¯ Both ACT 2 and ACT 3 FPGAs use two types of logic module.
C-Module
D00
D01
D10
D11
S-Module (ACT 2)
Y
A1
B1
A0
B0
D00
D01
D10
D11
OUT
S1
A1
B1
S0
A0
CLR
S-Module (ACT 3)
D00
D01
D10
D11
SE
Y
Q
A1
B1
S1
S0
S0
(b)
(c)
SE (sequential element)
1
D
C2
C1
CLR
0
Q
S1
A0
B0
CLR
CLK
CLK
(a)
SE
Y
SE
1
Z
0
S
master
latch
combinational
logic for clock
and clear
D
Z
Q
S
slave
latch
D
CLK
C2
C1
CLR
CLR
flip-flop macro
D
CLK
(d)
1D
Q
Q
Q
C1
(e)
(a) The C-module used by both ACT 2 and ACT 3 FPGAs. (b) The ACT 2 S-module. (c) The ACT 3
S-module. (d) Equivalent circuit of the SE. (e) The sequential element configured as a positive-edgetriggered D flip-flops.
4
Routing Architecture of ACT Family
¯ A row-based architecture.
¯ Each horizontal channel consists of a number of routing tracks.
¯ Some routing tracks are segmented where adjacent segments can be connected
through antifuses to form longer lines.
¯ There are also some vertical tracks running through the logic modules and horizontal channels.
5
FILENAME.APP=6822FG13.PS
I/O module
Antifuses
Vertical segments
Segmented
routing
channels
Rows of
logic
modules
Routing architecture of an Actel ACT FPGA.
6
Xilinx LCA Family
¯ The Xilinx LCA family employs LUT-based logic cells.
¯ A symmetrical array architecture is used.
Interconnect
Logic cell
7
Configurable Logic Block of LCA Family
¯ We consider the XC4000 devices for an example.
¯ The XC4000 FPGAs use a single type of configurable logic block (CLB).
¯ Each CLB contains two 4-input LUTs that feed a 3-input LUT. This allows a CLB to
implement any two logic functions with four or less variables, or some function with
five or more variables.
¯ A CLB can also be configured to be used as memory e.g. as two 16¢1 memory
SRAMs.
¯ The outputs of the function generators can be optionally stored in flip-flops inside a
CLB.
8
6-37
Figure 6-32 Simplified Diagram of a Xilinx® Configurable Logic Block
(Adapted with permission of Xilinx®, Inc.)
H1
G1
Look up Table
for G'
G2
G'
DIN
S/R
EC
MUX
G3
G4
•
16 bits of SRAM
S/R
Control
•
DIN
PRE
F'
•
•
Look up Table
for H'
D
H' S
EC
CLR
M M
H'
•
MUX
M
•
8 bits of SRAM
S
MUX
•
YQ
G'
•
1
M
G'
•
Y
H'
S
F1
Look up Table
for F'
F2
M
•
F'
MUX
F3
F4
S/R
Control
DIN
16 bits of SRAM
•
PRE
F'
D
XQ
G'
•
H' S
EC
CLR
M M
MUX
M
K (CLOCK)
•
S
MUX
1
M
F'
X
H'
S
M
- SRAM cell
M
9
Routing Architecture of LCA Family
¯ A typical Xilinx LCA FPGA consists of a two-dimensional array of CLBs with horizontal routing channels between rows of blocks and vertical routing channels between columns.
¯ Routing tracks are segmented which can be interconnected inside the switch matrices.
¯ Each interconnect point inside a switch matrix is formed by 6 pass transistors to
allow connections between adjacent segments and/or between the vertical and
horizontal lines that meet there.
10
T-153
Xilinx® XC4000™ FPGA Structure (Adapted with Permission of
Xilinx, Inc.)
•••
Long lines
•••
Single length
- Input/Output Block (IOB)
- Configurable logic block (CLB)
- Switch matrix
11
M
M
M
M
M
M
a
b
c
d
e
(a)
(b)
(a) A switch matrix. (b) Example of connections made through a switch matrix.
12
Altera MAX 5000 & 7000 Family
¯ The Altera MAX family employs PAL-based logic cells.
¯ The logic cells are called macrocells.
¯ A hierarchical PLD architecture is used where the macrocells are grouped into
larger blocks called logic array blocks.
PLD block
Chipwide interconnect
13
Logic Array Block of MAX Family
¯ Each logic array block (LAB) contains 16 macrocells.
¯ A simplified macrocell showing its basic PLD-like combinational logic structure:
...
¯ See Fig. 3.5 of text for the complete structure of a macrocell.
¯ In addition to the basic combinational logic structure shown above
– each macrocell has a flip-flop
– there are special connections that allow sharing of product terms between different macrocells in the same LAB.
14
Routing Architecture of MAX 5000 & 7000 Family
¯ The LABs are interconnected by a chipwide interconnect called programmable interconnect array (PIA).
¯ The PIA acts as a global bus and is built such that the connections between different
pairs of LABs all have the same delay.
15
T-150
Altera® MAX 7000™ Structure (Reprinted with Permission of
Altera Corporation,© Altera Corp., 1991)
I/O control block
Logic
array
block
Logic
array
block
Logic
array
block
Logic
array
block
Programmable interconnect array
I/O
control
block
Logic
array
block
Logic
array
block
Logic
array
block
Logic
array
block
Logic
array
block
Logic
array
block
Logic
array
block
Logic
array
block
Logic
array
block
Logic
array
block
Logic
array
block
Logic
array
block
I/O
control
block
I/O control block
16
Comparison of FPLD Families
Programming
technology
Architecture
Logic cell type
Interconnect
Interconnect
delay
Basic
logic cells
Logic cell
contents
Actel ACT 3
antifuse
Xilinx XC4000
SRAM
Altera MAX 7000
EPROM
row-based
multiplexer-based
segmented channels
symmetrical array
LUT-based
segmented channels with
switch matrices
variable
hierarchical-PLD
PAL-based
programmable interconnection
architecture
fixed
Configurable
Logic Block (CLB)
3 LUTs,
2 D flip-flops,
10 MUXes.
16 macrocells
in a LAB
Macrocell:
5 ANDs, 1 OR, 1 EXOR,
1 flip-flop, 3 MUXes.
Two or one.
Any two 4-input functions,
or one selected function
of
9 inputs.
64 CLBs (XC4002XL)
to
3136 CLBs (XC4085XL)
Multiple wide input
functions per LAB
variable
Combinational
functions
per logic cell
C-module and
S-module
C-module: 4:1 MUX,
2-input OR, 2-input AND.
S-module: 4:1 MUX, 2-input OR,
2-input AND, latch/D flip-flop.
One.
Most 3-and 4-input
functions.
Basic
logic cells
per chip
104 S+96 C (A1415)
to
697 S+680 C (A14100)
32 macrocells (EPM7032)
to
256 macrocells (EPM70256E)
17