Data Sheet
June 1999
ORCA Series 3C and 3T FPGAs
Clocks in the PICs
Clock Distribution Network (continued)
Because the Series 3 FPGAs have latches and FFs in
the I/Os, it is necessary to have clock signal distribution
to the PIOs as well as in the PLC array. The system
clock, the fast clock, and the ExpressCLK are available
for PIO clocking.
Clock Sources to the PLC Array
The source of a clock that is globally available to the
PLC array can be from any user I/O pad, any of the
ExpressCLK pads, or an internally generated source.
System Clock
PIC System Clock
As described in the Programmable Input/Output Cells
section, PICs are grouped in adjacent pairs. Any one of
the eight pads in a PIC pair can drive a clock spine in a
row or column. For PIC pairs on the top of the chip, the
column associated with the left PIC has the clock
spine, for pairs on the bottom, the right PIC column has
the spine. The top PIC of the pair sources the spine
from the left side of the array, and the bottom PIC of the
pair sources the spine from the right side of the array.
Clock delay and skew are minimized by having a single
clock buffer per pair of PICs. The clock spine for each
pair can also be driven by one of the four PIC switching
segments (pSW) in each PIC of the pair. This allows a
signal generated in the PLC array to be routed onto the
global clock spine network. The system clock output of
the programmable clock manager (PCM) may also be
routed to the global system clock spines via the pSW
segments. Figure 33 shows the clock spine multiplex-
ing structure for a pair of PICs on the top of the array.
There are five local system clock lines in each PIC.
Much like the sources for a clock in the PFU, two of the
local PIC clocks are generated within the PIC from long
lines. One is generated from the set of ten PIC long
lines (pxL) that runs parallel to the PICs on a side, and
the other is generated from the set of ten long lines (xL)
from the PLC array that terminate in the PIC. Another
local PIC system clock route comes from the set of ten
xL lines in the adjacent PLC that is parallel to the side
of the array on which the PIC resides. The fourth local
PIC system clock route comes from the set of ten long
lines (xL) from the PLC array that terminate in the adja-
cent PIC that is not part of the same PIC pair. Much like
the E1 signals in the PLCs that are used to distribute a
local clock to the PFU source, the fifth local clock line in
each PIC comes from local pSW signals. This clock
signal for each PIC is shown in Figure 33. One of these
five local PIC system clocks is selected for the system
clock signal in the PIO. It is used as the PIO system
clock for both input and output clocking as selected
within the PIO. All PIOs in a PIC share the same sys-
tem clock.
Fast Clock
The fast clock spines are sourced to the PLC array
from each side of the device by the ExpressCLK pads
via the CLKCNTRL function block (described in the
Special Function Blocks section). The ExpressCLK and
fast clock source from the pads is shown in Figure 34
and will be described further in the ExpressCLK Inputs
subsection.
PIC ExpressCLK
The ExpressCLK signal used at the PIC latches/FFs
comes from the CLKCNTRL function block that resides
in the middle of the side on which the PIC resides. A
single signal comes from the CLKCNTRL and is driven
by separate buffers onto two ExpressCLK long wires.
One of these ExpressCLK signals goes to the PICs on
the right of (above) the CLKCNTRL block, and the
other ExpressCLK signal goes to the PICs on the left of
(below) the CLKCNTRL block on that side.
PAD A
PAD B
PAD C
PAD D
pSW[4]
pSW[5]
pSW[6]
pSW[7]
TO LOCAL CLOCKS
TO LOCAL CLOCKS
TPICR
SPINE
TPICL
5-5800(F)
Figure 33. PIC System Clock Spine Generation
52
Lucent Technologies Inc.
AGERE [ AGERE SYSTEMS ]
