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Lucent Technologies Inc.
75
Preliminary Data Sheet, Rev. 1
September 1998
ORCA Series 3 FPGAs
Programmable Clock Manager (PCM):
Advance Information (continued)
PCM/FPGA Internal Interface
Writing and reading the PCM registers is done through
a simple asynchronous interface that connects with the
FPGA routing resources. Reads from the PCM by the
FPGA logic are accomplished by setting up the 3-bit
address, A[2:0], and then applying an active-high read
enable (RE) pulse. The read data will be available as
long as RE is held high. The address may be changed
while RE is high, to read other addresses. When RE
goes low, the data output bus is 3-stated.
Writes to the PCM by the FPGA logic are performed by
applying the write data to the data input bus of the
PCM
, applying the 3-bit address to write to, and assert-
ing the write enable (WE) signal high. Data will be writ-
ten by the high-going transition of the WE pulse.
The read enable (RE) and write enable (WE) signals
may not be active at the same time. For detailed timing
information and specifications, see the Timing Charac-
teristics section of this data sheet.
The LOCK signal output from the PCM to the FPGA
routing indicates a stable output clock signal from the
PCM
. The LOCK signal is high when the PCM output
clock parameters fall within the programmed values
and the PCM specifications for jitter. Due to phase cor-
rections that occur internal to the PCM, the LOCK sig-
nal might occasionally pulse low when the output clock
is out of specification for only one or two clock cycles
(high jitter due to temperature, voltage fluctuation, etc.)
To accommodate these pulses, it is suggested that the
user integrate the LOCK signal over a period suitable
to their application to achieve the desired usage of the
LOCK signal.
The LOCK signal will also pulse high and low during
the acquisition time as the output clock stabilizes. True
LOCK is only achieved when the LOCK signal is a solid
high. Again, it is suggested that the user integrate the
LOCK signal over a time period suitable to the subject
application.
PCM Operation
Several features are available for the control of the
PCM
’s overall operation. The PCM may be program-
mably enabled/disabled via bit 0 of register seven.
When disabled, the analog power supply of the PCM is
turned off, conserving power and eliminating the possi-
bility of inducing noise into the system power buses.
Individual bits (register seven, bits [2:1]) are provided
to reset the DLL and PLL functions of the PCM. These
resets affect only the logic generating the DLL or PLL
function; they do not reset the divider values (DIV0,
DIV1, DIV2) or registers [7:0]. The global set/reset
(GSRN) is also programmably controlled via register
seven, bit 7. If register seven, bit 7 is set to 1, GSRN
will have no effect on the PCM logic, allowing the clock
to operate during a global set/reset. This function
allows the FPGA to be reset without affecting a clock
that is sent off-chip and used elsewhere in the system.
Bit 6 of register seven affects the functionality of the
PCM
during configuration. If set to 1, this bit enables
the PCM to operate during configuration, after the PCM
has been configured. The PCM functionality is pro-
grammed via the bit stream. If register seven, bit 6 is 0,
the PCM cannot function and its power supply is dis-
abled until after the configuration DONE signal goes
high.
When the PCM is powered up via register seven, bit 0,
there is a wake-up time associated with its operation.
Following the wake-up time, the PCM will begin to fully
function, and, following an acquisition time during
which the output clock may be unstable, the PCM will
be in steady-state operation. There is also a shutdown
time associated with powering off the PCM. The output
clock will be unstable during this period. Waveforms
and timing parameters can be found in the Timing
Characteristics section of this data sheet.