2–62
Altera Corporation
Stratix II GX Device Handbook, Volume 2
October 2007
Receiver Modules
and the
rx_pll_locked
signal is ignored when the CRU is in
lock-to-data mode.
Table 2–15
lists the specifications for the clock
recovery unit.
Table 2–16
lists the available /M and /L values within the
receiver PLL.
Clock Synthesis
The maximum input frequency of the receiver PLL’s phase frequency
detector (PFD) is 325 MHz. To achieve a reference clock frequency above
this limitation, the divide by 2 pre-divider on the dedicated local
REFCLK
path is automatically enabled by the Quartus II software. This divides the
reference clock frequency by a factor of 2, and the /M PLL multiplier
multiplies this pre-divided clock to yield the configured data rate. For
example, in a situation with a data rate of 2,488 Mbps and a reference
clock of 622 MHz, the reference clock must be assigned to the
REFCLK
port where the 622-MHz reference clock can be divided by 2, yielding a
311-MHz clock at the PFD. The VCO runs at half the data rate, so the
selected multiplication factor should yield a 1244 MHz high-speed clock.
The Quartus II software automatically selects a multiplication factor of 4
in this case to generate a 1244 MHz clock from the pre-divided 311 MHz
clock.
If the /2 pre-divider is used, the reference clock must be fed by a
dedicated reference clock input (
REFCLK
) pin. Otherwise the Quartus II
compiler gives a fitter error.
The pre-divider and the multiplication factors are automatically set by the
Quartus II software. The MegaWizard takes the data rate input and
provides a list of the available reference clock frequencies that fall within
the supported multiplication factors that you can select.
Table 2–15. Clock Recovery Unit Specifications
Parameter
Specifications
Input reference frequency range
50 MHz to 622.08 MHz
Data rate support
600 Mbps to 6.375 Gbps
Table 2–16. Available /M and /L Values Within the Receiver PLL
RX PLL Reference Clock Source
/M
/L
rx_cruclk
1, 4, 5, 8, 10, 16,
20, 25
1, 2, 4
Содержание Stratix II GX
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