MPC8641DEC datasheet(17/140 Pages) FREESCALE

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MPC8641 and MPC8641D Integrated Host Processor Hardware Specifications, Rev. 1

Freescale Semiconductor

Input Clocks

It is imperative to note that the processor’s minimum and maximum SYSCLK, core, and VCO frequencies

must not be exceeded regardless of the type of clock source. Therefore, systems in which the processor is

operated at its maximum rated e600 core frequency should avoid violating the stated limits by using

down-spreading only.

SDn_REF_CLK and SDn_REF_CLK was designed to work with a spread spectrum clock (+0 to 0.5%

spreading at 30-33kHz rate is allowed), assuming both ends have same reference clock. For better results

use a source without significant unintended modulation.

4.2

Real Time Clock Timing

The RTC input is sampled by the platform clock (MPX clock). The output of the sampling latch is then

used as an input to the counters of the PIC. There is no jitter specification. The minimum pulse width of

the RTC signal should be greater than 2x the period of the MPX clock. That is, minimum clock high time

is 2

× tMPX, and minimum clock low time is 2 × tMPX. There is no minimum RTC frequency; RTC may be

grounded if not needed.

4.3

eTSEC Gigabit Reference Clock Timing

Table 10 provides the eTSEC gigabit reference clocks (EC1_GTX_CLK125 and EC2_GTX_CLK125) AC

timing specifications for the MPC8641.

Table 9. Spread Spectrum Clock Source Recommendations

At recommended operating conditions. See Table 2.

Parameter

Min

Max

Unit

Notes

Frequency modulation

—

kHz

Frequency spread

—

1.0

1, 2

Notes:

1. Guaranteed by design.

2. SYSCLK frequencies resulting from frequency spreading, and the resulting core and VCO

frequencies, must meet the minimum and maximum specifications given in Table 8.

Table 10. EC

n_GTX_CLK125 AC Timing Specifications

Parameter/Condition

Symbol

Min

Typical

Max

Unit

Notes

n_GTX_CLK125 frequency

fG125

—

125 ±100

ppm

—MHz

n_GTX_CLK125 cycle time

tG125

—8

—

n_GTX_CLK125 peak-to-peak jitter

tG125J

—

250

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