Data Sheet
June 1999
ORCA Series 3C and 3T FPGAs
The clock routing segments are designed to be a clock
spine. In each PLC, there is a fast connection available
from the clock segment to a long-line driver (described
earlier). With this connection, one of the clock routing
segments in each PLC can be used to drive one of the
ten xL routing segments perpendicular to it, which, in
turn, creates a clock spine tree. This feature is dis-
cussed in detail in the Clock Distribution Network sec-
tion.
Programmable Logic Cells (continued)
xL Routing Lines. The xL routing lines run vertically
and horizontally the height and width of the array,
respectively. There are a total of 20 xL routing lines per
PLC: ten horizontal (hxL[9:0]) and ten vertical
(vxL[9:0]). Each of the xL lines connects to the PIC
routing at either end. The xL lines are intended prima-
rily for global signals that must travel long distances
and require minimum delay and/or skew, such as
clocks or 3-state buses.
Special connectivity is provided in each PLC to connect
the clock enable signals (CE and ASWE) and the LSR
signal to the clock network for fast global control signal
distribution. CE and ASWE have a special connection
to the horizontal clock spine, and LSR has a special
connection to the vertical clock spine. This allows both
signals to be routed globally within the same PLC, if
desired; however, this will consume some of the
resources available for clock signal routing.
Each xL line (also called a long line) drives a buffer in
each PLC that can drive onto the horizontal and verti-
cal local clock routing segments (lCLK) in the PLC.
Also, two out of each group of ten xL segments in each
PLC can be driven by a buffer attached to a clock spine
(described later) allowing local distribution of global
clock signals. More general-purpose connections to the
long lines can be made through the xBID segments in a
PLC. Each long line is connected to an xBID segment
on a bit-by-bit basis. These BIDI connections allow cor-
ner turning from horizontal to vertical long lines, and
connection between long lines and x1 or x5 segments.
If using these spines, the clock enable signal must
come from the right or left edge of the device, and the
LSR signal must come from the top or bottom of the
device due to their horizontal and vertical connectivity,
respectively, to the clock network.
xH Routing Segments. Ten by-half (xH) routing seg-
ments run horizontally (hxH[9:0]) and ten xH routing
segments run vertically (vxH[9:0]) in each row and col-
umn in the array. These routing segments travel a dis-
tance of one-half the PLC array before being broken in
the middle of the array in the interquad area (discussed
later). They also connect at the periphery of the FPGA
to the PICs, like the xL lines. xH routing segments con-
nect to the PLCs only by switching segments. They are
intended for fast signal interconnect.
Minimizing Routing Delay
The CIP is an active element used to connect two rout-
ing segments. As an active element, it adds signifi-
cantly to the resistance and capacitance of a routing
network (net), thus increasing the net’s delay. The
advantage of the x1 segment over an x5 segment is
routing flexibility. A net from one PLC to the next is eas-
ily routed by using x1 routing segments. As more CIPs
are added to a net, the delay increases. To increase
speed, routes that are greater than two PLCs away are
routed on the x5 routing segments because a CIP is
located only in every fifth PLC. A net that spans eight
PLCs requires seven x1 routing segments and six
CIPs. Using x5 routing segments, the same net uses
two routing segments and one CIP.
Clock (and Global CE and LSR) Routing Segments.
For a very fast and low-skew clock (or other global sig-
nal tree), clock routing segments run the entire height
and width of the PLC array. There are two clock routing
segments per PLC: one horizontal (hCLK) and one ver-
tical (vCLK). The source for these clock routing seg-
ments can be any of the I/O buffers in the PIC, the
Series 3 ExpressCLK inputs, user logic, or the pro-
grammable clock manager (PCM). The horizontal clock
routing segments (hCLK) are alternately driven by the
left and right PICs. The vertical clock routing segments
(vCLK) are alternately driven by the top and bottom
PICs.
Lucent Technologies Inc.
33
AGERE [ AGERE SYSTEMS ]
