DSP56367 datasheet(29/100 Pages) FREESCALE

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External Clock Operation

DSP56367 Technical Data, Rev. 2.1

Freescale Semiconductor

3-5

3.7

External Clock Operation

The DSP56367 system clock is an externally supplied square wave voltage source connected to

EXTAL(Figure 3-1).

Figure 3-1 External Clock Timing

Internal clock cycle time with PLL disabled

—2

× ETC

—

Instruction cycle time

ICYC

—TC

—

1 DF = Division Factor

Ef = External frequency

ETC = External clock cycle

MF = Multiplication Factor

PDF = Predivision Factor

TC = internal clock cycle

2 Refer to the DSP56300 Family Manual for a detailed discussion of the PLL.

Table 3-5 Clock Operation

No.

Characteristics

Symbol

Min

Max

Frequency of EXTAL (EXTAL Pin Frequency)

The rise and fall time of this external clock should be 2 ns maximum.

2.0 ns

150.0

EXTAL input high1, 2

• With PLL disabled (46.7%–53.3% duty cycle3)

• With PLL enabled (42.5%–57.5% duty cycle3)

ETH

3.11 ns

2.83 ns

∞

157.0

µs

EXTAL input low1, 2

• With PLL disabled (46.7%–53.3% duty cycle3)

• With PLL enabled (42.5%–57.5% duty cycle3)

ETL

3.11 ns

2.83 ns

∞

157.0

µs

Table 3-4 Internal Clocks (continued)

Characteristics

Symbol

Expression1, 2

Min

Typ

Max

EXTAL

VILC

VIHC

Midpoint

Note: The midpoint is 0.5 (VIHC + VILC).

ETH

ETL

ETC

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