Detailed Specifications
2- 76
R e v i sio n 1 8
single-ended, or voltage-referenced standard. The [H]CLKxN pad can only be used as a differential pair
with [H]CLKxP.
The block marked “/i Delay Match” is a fixed delay equal to that of the i divider. The “/j Delay Match” block
has the same function as its j divider counterpart.
Functional Description
that allow frequency scaling of the clock signal:
The i divider in the feedback path allows multiplication of the input clock by integer factors ranging
from 1 to 64, and the resultant frequency is available at the output of the PLL block.
The j divider divides the PLL output by integer factors ranging from 1 to 64, and the divided clock
is available at CLK1.
The two dividers together can implement any combination of multiplication and division up to a
maximum frequency of 1 GHz on CLK1. Both the CLK1 and CLK2 outputs have a fixed 50/50
duty cycle.
The output frequencies of the two clocks are given by the following formulas (fREF is the reference
clock frequency):
fCLK1 = fREF * (DividerI) / (DividerJ)
EQ 4
fCLK2 = fREF * (DividerI)
EQ 5
CLK2 provides the PLL output directly—without division
The input and output frequency ranges are selected by LowFreq and Osc(2:0), respectively. These
delayed (using the five DelayLine bits) relative to the reference clock (or vice versa) by up to 3.75 ns in
are independent of frequency, so this results in phase changes that vary with frequency. The delay value
is highly dependent on VCC and the speed grade.
Figure 2-49 is a logical diagram of the various control signals to the PLL and shows how the PLL
interfaces with the global and routing networks of the FPGA. Note that not all signals are user-
accessible. These non-user-accessible signals are used by the place-and-route tool to control the
configuration of the PLL. The user gains access to these control signals either based upon the
into the design. For example, connecting the macro PLLOUT to CLK2 will control the OUTSEL signal.
Note:
Not all signals are available to the user.
Figure 2-49 PLL Logical Interface
RefCLK
FB
CLK1
CLK2
REFSEL
ROOTSEL
FBMuxSEL
[H]CLKINT
[H]CLKxP
[H]CLKxN
I/O
Core net
CLK net
FBINT
0
1
2
3
CLKINT
CLK1 (PLLn-1)
[H]CLK
To PLLn+1
PLLSEL
OUTSEL
CLK Out
(Routed net out pin)
PLL