PPC440EPX-NPAFFFTS AMCC [Applied Micro Circuits Corporation], PPC440EPX-NPAFFFTS Datasheet - Page 75

• Manufacturer Part Number: PPC440EPX-NPAFFFTS
• Description: PowerPC 440EPx Embedded Processor
• Manufacturer: AMCC [Applied Micro Circuits Corporation]

Revision 1.26 – October 15, 2007
Spread Spectrum Clocking
Care must be taken when using a spread spectrum clock generator (SSCG) with the PPC440EPx. This controller
uses a PLL for clock generation inside the chip. The accuracy with which the PLL follows the SSCG is referred to
as tracking skew. The PLL bandwidth and phase angle determine how much tracking skew there is between the
SSCG and the PLL for a given frequency deviation and modulation frequency. When using an SSCG with the
PPC440EPx the following conditions must be met:
Notes:
Important:
requirements and does not adversely affect other aspects of the system.
AMCC Proprietary
Preliminary Data Sheet
• The frequency deviation must not violate the minimum clock cycle time. Therefore, when operating the
• The maximum frequency deviation cannot exceed −3%, and the modulation frequency cannot exceed 40 kHz.
• Use the Peripheral Bus Clock for logic that is synchronous to the peripheral bus since this clock tracks the
• Use the DDR SDRAM MemClkOut since it also tracks the modulation.
PPC440EPx with one or more internal clocks at their maximum supported frequency, the SSCG can only lower
the frequency.
In some cases, on-board PPC440EPx peripherals impose more stringent requirements.
modulation.
1. The serial port baud rates are synchronous to the modulated clock. The serial port has a tolerance of
2. Ethernet operation is unaffected.
3. IIC operation is unaffected.
approximately 1.5% on baud rate before framing errors begin to occur. The 1.5% tolerance assumes that
the connected device is running at precise baud rates.
It is up to the system designer to ensure that any SSCG used with the PPC440EPx meets the above
440EPx – PPC440EPx Embedded Processor
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