Data Sheet
June 1999
ORCA Series 3C and 3T FPGAs
ExpressCLK that feeds the CLKCNTRL blocks on the
two sides adjacent to the PCM, and one to the system
clock spine network through general routing. Figure 45
shows a high-level block diagram of the PCM.
Programmable Clock Manager (PCM)
The ORCA programmable clock manager (PCM) is a
special function block that is used to modify or condi-
tion clock signals for optimum system performance.
Some of the functions that can be performed with the
PCM are clock skew reduction (both internal and board
level), duty-cycle adjustment, clock delay reduction,
clock phase adjustment, and clock frequency multipli-
cation/division. Due to the different capabilities required
by customer application, each PCM contains both a
PLL (phase-locked loop) and a DLL (delayed-locked
loop) mode. By using PLC logic resources in conjunc-
tion with the PCM, many other functions, such as fre-
quency synthesis, are possible.
Functionality of the PCM is programmed during opera-
tion through a read/write interface internal to the FPGA
array or via the configuration bit stream. The internal
FPGA interface comprises write enable and read
enable signals, a 3-bit address bus, an 8-bit input (to
the PCM) data bus, and an 8-bit output data bus. There
is also a PCM output signal, LOCK, that indicates a sta-
ble output clock state. These signals are used to pro-
gram a series of registers to configure the PCM
functional core for the desired functionality.
Operation of the PCM is divided into two modes, delay-
locked loop (DLL) and phase-locked loop (PLL). Some
operations can be performed by either mode and some
are specific to a particular mode. These will be
described in each individual mode section. In general,
DLL mode is preferable to PLL mode for the same func-
tion because it is less sensitive to input clock noise.
There are two PCMs on each Series 3 device, one in
the lower left corner and one in the upper right corner.
Each can drive two different, but interrelated clock net-
works inside the FPGA. Each PCM can take a clock
input from the ExpressCLK pad in its corner or from
general routing resources. There are also two input
sources that provide feedback to the PCM from the
PLC array. One of these is a dedicated corner Express-
CLK feedback, and the other is from general routing.
Each PCM sources two clock outputs, one to the corner
In the discussions that follow, the duty cycle is the per-
cent of the clock period during which the output clock is
high.
USER CONTROL SIGNALS
PCM-FPGA
INTERFACE
CORNER EXPRESSCLK IN
EXPRESSCLK OUT
PCM CORE
FUNCTIONS
SYSTEM CLOCK OUT
(TO GENERAL ROUTING)
GENERAL CLOCKIN
(FROM GENERAL ROUTING)
FEEDBACK
ExpressCLK
FEEDBACK CLOCK
FROM ROUTING
5-5828(F)
Figure 45. PCM Block Diagram
72
Lucent Technologies Inc.
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