
22
Lucent Technologies Inc.
Data Sheet
June 1999
ORCA Series 2 FPGAs
Programmable Logic Cells
 (continued)
PLC Architectural Description
Figure 23 is an architectural drawing of the PLC which 
reflects the PFU, the lines, and the CIPs. A discussion 
of each of the letters in the drawing follows. 
A
. These are switching lines which give the router flexi-
bility. In general switching theory, the more levels of 
indirection there are in the routing, the more routable 
the network is. The switching lines can also connect 
to adjacent PLCs.
The switching lines provide direct connections to 
PLCs directly to the top, bottom, left, and right, with-
out using other routing resources. The ability to dis-
able this connection between PLCs is provided so 
that each side of these connections can be used 
exclusively as switching lines in their respective 
PLC.
B
. These CIPs connect the X1 routing. These are 
located in the middle of the PLC to allow the block to 
connect to either the left end of the horizontal X1 line 
from the right or the right end of the horizontal X1 
line from the left, or both. By symmetry, the same 
principle is used in the vertical direction. The X1 
lines are not twisted, making them suitable for data 
paths. 
C
. This set of CIPs is used to connect the X1 and X4 
nets to the switching lines or to other X1 and X4 
nets. The CIPs on the major diagonal allow data to 
be transmitted from X1 nets to the switching lines 
without being scrambled. The CIPs on the major 
diagonal also allow unscrambled data to be passed 
between the X1 and X4 nets.
In addition to the major diagonal CIPs for the X1 
lines, other CIPs provide an alternative entry path 
into the PLC in case the first one is already used. 
The other CIPs are arrayed in two patterns, as 
shown. Both of these patterns start with the main 
diagonal, but the extra CIPs are arrayed on either a 
parallel diagonal shifted by one or shifted by two 
(modulo the size of the vertical bus (5)). This allows 
any four application nets incident to the PLC corner 
to be transferred to the five switching lines in that 
corner. Many patterns of five nets can also be trans-
ferred.
D
. The X4 lines are twisted at each PLC. One of the 
four X4 lines is broken with a CIP which allows a sig-
nal to be routed a distance of four PLCs in any direc-
tion on a single line without an intermediate CIP The 
X4 lines are less populated with CIPs than the X1 
lines to increase their speed. A CIP can be enabled 
to extend an X4 line four more PLCs, and so on.
For example, if an application signal is routed onto 
HX4[4] in a PLC, it appears on HX4[5] in the PLC to 
the right. This signal step-up continues until it 
reaches HX4[7], two PLCs later. At this point, the 
user can break the connection or continue the signal 
for another four PLCs.
E
. These symbols are bidirectional buffers (BIDIs). 
There are four BIDIs per PLC, and they provide sig-
nal amplification as needed to decrease signal 
delay. The BIDIs are also used to transmit signals on 
XL lines.
F
. These are the BIDI and BIDIH controllers. The 3-
state control signal can be disabled. They can be 
configured as active-high or active-low indepen-
dently of each other.
G
.This set of CIPs allows a BIDI to get or put a signal 
from one set of switching lines on each side. The 
BIDIs can be accessed by the switching lines. These 
CIPs allow a nibble of data to be routed though the 
BIDIs and continue to a subsequent block. They also 
provide an alternative routing resource to improve 
routability.
H
.These CIPs are used to take data from/to the BIDIs 
to/from the XL lines. These CIPs have been opti-
mized to allow the BIDI buffers to drive the large load 
usually seen when using XL lines.
I
. Each latch/FF can accept data: from an LUT output; 
from a direct data input signal from general routing; 
or, as in the case of PLCs located in the two rows 
(columns) adjacent to PICs, directly from the pad. In 
addition, the LUT outputs can bypass the latches/
FFs completely and output data on the general rout-
ing resources. The four inputs shown are used as 
the direct input to the latches/FFs from general rout-
ing resources. If the LUT is in memory mode, the 
four inputs WD[3:0] are the data input to the mem-
ory.