ppc440gr-3jb667cz Applied Micro Circuits Corporation (AMCC), ppc440gr-3jb667cz Datasheet - Page 69

• Manufacturer Part Number: ppc440gr-3jb667cz
• Description: Powerpc 440gr Embedded Processor
• Manufacturer: Applied Micro Circuits Corporation (AMCC)

Spread Spectrum Clocking
Care must be taken when using a spread spectrum clock generator (SSCG) with the PPC440GR. 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
PPC440GR the following conditions must be met:
Notes:
Important:
AMCC Proprietary
440GR – PPC440GR Embedded Processor
• 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 40kHz.
• 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.
PPC440GR with one or more internal clocks at their maximum supported frequency, the SSCG can only lower
the frequency.
In some cases, on-board PPC440GR 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 PPC440GR meets the above
requirements and does not adversely affect other aspects of the system.
Preliminary Data Sheet
Revision 1.19 – May 07, 2008
69