MPC8640DEC datasheet(15/140 Pages) FREESCALE

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MPC8640 and MPC8640D Integrated Host Processor Hardware Specifications, Rev. 1

Freescale Semiconductor

Input Clocks

4.1

System Clock Timing

Table 7 provides the system clock (SYSCLK) AC timing specifications for the MPC8640.

4.1.1

SYSCLK and Spread Spectrum Sources

Spread spectrum clock sources are an increasingly popular way to control electromagnetic interference emissions

(EMI) by spreading the emitted noise to a wider spectrum and reducing the peak noise magnitude in order to meet

industry and government requirements. These clock sources intentionally add long-term jitter in order to diffuse the

EMI spectral content. The jitter specification given in Table 7 considers short-term (cycle-to-cycle) jitter only and

the clock generator’s cycle-to-cycle output jitter should meet the MPC8640 input cycle-to-cycle jitter requirement.

Frequency modulation and spread are separate concerns, and the MPC8640 is compatible with spread spectrum

sources if the recommendations listed in Table 8 are observed.

Table 7. SYSCLK AC Timing Specifications

At recommended operating conditions (see Table 2) with OVDD = 3.3 V ± 165 mV.

Parameter/Condition

Symbol

Min

Typical

Max

Unit

Notes

SYSCLK frequency

fSYSCLK

—

166.66

MHz

SYSCLK cycle time

tSYSCLK

6—

—

SYSCLK rise and fall time

tKH, tKL

0.61.0

1.2ns

SYSCLK duty cycle

tKHK/tSYSCLK

—

SYSCLK jitter

—

150

4, 5

Notes:

1. Caution: The MPX clock to SYSCLK ratio and e600 core to MPX clock ratio settings must be chosen such that the

resulting SYSCLK frequency, e600 (core) frequency, and MPX clock frequency do not exceed their respective

maximum or minimum operating frequencies. Refer toSection 18.2, “MPX to SYSCLK PLL Ratio”, and

Section 18.3, “e600 to MPX clock PLL Ratio”, for ratio settings.

2. Rise and fall times for SYSCLK are measured at 0.4 V and 2.7 V.

3. Timing is guaranteed by design and characterization.

4. This represents the short term jitter only and is guaranteed by design.

5. The SYSCLK driver’s closed loop jitter bandwidth should be <500 kHz at -20 dB. The bandwidth must be set low to

allow cascade-connected PLL-based devices to track SYSCLK drivers with the specified jitter. Note that the

frequency modulation for SYSCLK reduces significantly for the spread spectrum source case. This is to guarantee

what is supported based on design.

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