R
XC5200 Series Field Programmable Gate Arrays
The XC5200 CLB consists of four LCs, as shown in
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 chal-
lenge 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 Local Interconnect
Matrix (LIM) and direct connects. These two interconnect
resources, combined with the CLB, form the VersaBlock,
represented in
The LIM provides 100% connectivity of the inputs and out-
puts of each LC in a given CLB. The benefit of the LIM is
that no general routing resources are required to connect
feedback paths within a CLB. The LIM connects to the
GRM via 24 bidirectional nodes.
The direct connects allow immediate connections to neigh-
boring CLBs, once again without using any of the general
interconnect. These two layers of local routing resource
improve the granularity of the architecture, effectively mak-
ing the XC5200 family a “sea of logic cells.” Each
Versa-Block has four 3-state buffers that share a common
enable line and directly drive horizontal and vertical Lon-
glines, creating robust on-chip bussing capability. The
VersaBlock allows fast, local implementation of logic func-
tions, effectively implementing user designs in a hierarchi-
cal fashion. These resources also minimize local routing
congestion and improve the efficiency of the general inter-
connect, which is used for connecting larger groups of
logic. It is this combination of both fine-grain and
coarse-grain architecture attributes that maximize logic uti-
lization in the XC5200 family. This symmetrical structure
takes full advantage of the third metal layer, freeing the
placement software to pack user logic optimally with mini-
mal routing restrictions.
LC3
DI
CO
DO
D
Q
F4
F3
F2
F1
FD
F
X
LC2
DO
DI
D
F4
F3
F2
F1
X
Q
VersaRing I/O Interface
The interface between the IOBs and core logic has been
redesigned in the XC5200 family. The IOBs are completely
decoupled from the core logic. The XC5200 IOBs contain
dedicated boundary-scan logic for added board-level test-
ability, but do not include input or output registers. This
approach allows a maximum number of IOBs to be placed
around the device, improving the I/O-to-gate ratio and
decreasing the cost per I/O. A “freeway” of interconnect
cells surrounding the device forms the VersaRing, which
provides connections from the IOBs to the internal logic.
These incremental routing resources provide abundant
connections from each IOB to the nearest VersaBlock, in
addition to Longline connections surrounding the device.
The VersaRing eliminates the historic trade-off between
high logic utilization and pin placement flexibility. These
incremental edge resources give users increased flexibility
in preassigning (i.e., locking) I/O pins before completing
their logic designs. This ability accelerates time-to-market,
since PCBs and other system components can be manu-
factured concurrent with the logic design.
FD
F
LC1
DO
DI
D
F4
F3
F2
F1
X
Q
FD
F
LC0
DO
DI
D
F4
F3
F2
F1
X
CI
CE CK
CLR
X4957
Q
FD
F
General Routing Matrix
The GRM is functionally similar to the switch matrices
found in other architectures, but it is novel in its tight cou-
pling to the logic resources contained in the VersaBlocks.
Advanced simulation tools were used during the develop-
ment of the XC5200 architecture to determine the optimal
level of routing resources required. The XC5200 family
contains six levels of interconnect hierarchy — a series of
Figure 4: Configurable Logic Block
7-86
November 5, 1998 (Version 5.2)
ETC [ ETC ]
