EP4SE360F35I4 Datasheet, PDF(155/432 Page) Altera Corporation – This section provides a complete overview of all features relating to the Stratix IV device family, which is the most architecturlly advanced

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EP4SE360F35I4 Datasheet, PDF (155/432 Pages) Altera Corporation – This section provides a complete overview of all features relating to the Stratix IV device family, which is the most architecturlly advanced

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Chapter 5: Clock Networks and PLLs in Stratix IV Devices

PLLs in Stratix IV Devices

5â39

Spread-Spectrum Tracking

Stratix IV devices can accept a spread-spectrum input with typical modulation

frequencies. However, the device cannot automatically detect that the input is a

spread-spectrum signal. Instead, the input signal looks like deterministic jitter at the

input of the PLL. Stratix IV PLLs can track a spread-spectrum input clock as long as it

is within input-jitter tolerance specifications. Stratix IV devices cannot internally

generate spread-spectrum clocks.

Clock Switchover

The clock switchover feature allows the PLL to switch between two reference input

clocks. Use this feature for clock redundancy or for a dual-clock domain application

such as in a system that turns on the redundant clock if the previous clock stops

running. The design can perform clock switchover automatically when the clock is no

longer toggling or based on a user control signal, clkswitch.

The following clock switchover modes are supported in Stratix IV PLLs:

â Automatic switchoverâThe clock sense circuit monitors the current reference

clock and if it stops toggling, automatically switches to the other inclk0 or inclk1

clock.

â Manual clock switchoverâClock switchover is controlled using the clkswitch

signal. When the clkswitch signal goes from logic low to logic high, and stays

high for at least three clock cycles, the reference clock to the PLL is switched from

inclk0 to inclk1, or vice-versa.

â Automatic switchover with manual overrideâThis mode combines automatic

switchover and manual clock switchover. When the clkswitch signal goes high, it

overrides the automatic clock switchover function. As long as the clkswitch signal

is high, further switchover action is blocked.

September 2012 Altera Corporation

Stratix IV Device Handbook

Volume 1

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