R
Table 3.
Routing Resource Comparison
XC5200
10
4
8
8
yes
XC4000
8
4
6
0
no
Architectural Overview
Figure 1 presents a simplified, conceptual overview of the
XC5200 architecture. Similar to conventional FPGAs, the
XC5200 family consists of programmable IOBs,
programmable logic blocks, and programmable
interconnect. Unlike other FPGAs, however, the logic and
local routing resources of the XC5200 family are
combined in flexible VersaBlocks. General-purpose
routing connects to the VersaBlock through the General
Routing Matrix (GRM).
VersaBlock: Abundant Local Routing Plus Versatile
Logic
The basic logic element in each VersaBlock structure is
the Logic Cell, shown in Figure 2. Each LC contains a 4-
input function generator (F), a storage device (FD), and
control logic. There are five independent inputs and three
outputs to each LC. The independence of the inputs and
outputs allows the software to maximize the resource
utilization within each LC. Each Logic Cell also contains a
direct feedthrough path that does not sacrifice the use of
either the function generator or the register; this feature is
a first for FPGAs. The storage device is configurable as
either a D flip-flop or a latch. The control logic consists of
carry logic for fast implementation of arithmetic functions,
which can also be configured as a cascade chain allowing
decode of very wide input functions.
The XC5200 CLB consists of four LCs, as shown in
Figure 3. Each CLB has 20 independent inputs and 12
independent outputs. The top and bottom pairs of LCs can
be configured to implement 5-input functions. The
challenge of FPGA implementation software has always
been to maximize the usage of logic resources. The
XC5200 family addresses this issue by surrounding each
CLB with two types of local interconnect — the LIM and
direct connects. These two interconnect resources,
combined with the CLB, form the VersaBlock, represented
in Figure 4.
Resource
Single-length Lines
Double-length Lines
Longlines
Direct Connects
VersaRing
• The TLM process allows significant improvements in the
routing structure. Each XC5200 VersaBlock element
has complete intra-CLB routing, the LIM, and offers four
direct routing connections to each of the four
neighboring CLBs (North, South, East, and West). Any
function generator or flip-flop thus has unrestricted
connectivity to 19 other function generators or flip-
flops: three in its own CLB, and 16 in the adjacent
CLBs. These direct connects do not compete with the
general routing resources (see Table 3).
• Each XC5200 3-state buffer (TBUF) can drive up to two
horizontal Longlines; each XC4000 TBUF accesses
only one horizontal Longline.
• There is a special racetrack, the VersaRing, between
the outer edge of the core CLB array and the ring of
IOBs, providing significant help in overcoming the
problems caused by early locking of I/O pins.
• There are no internal pull-ups for XC5200 Longlines.
Input/Output Blocks (IOBs)
VersaRing
GRM
Versa-
Block
GRM
Versa-
Block
GRM
Versa-
Block
CO
VersaRing
GRM
Versa-
Block
GRM
Versa-
Block
GRM
Versa-
Block
VersaRing
DO
DI
D
Q
GRM
Versa-
Block
GRM
Versa-
Block
GRM
Versa-
Block
F4
F3
F2
F1
FD
F
X
VersaRing
X4955
CI
CE CK
CLR
X4956
Figure 1.
XC5200 Architectural Overview
Figure 2.
XC5200 Logic Cell (Four LCs per CLB)
3
XILINX [ XILINX, INC ]
