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APPLICATION INFORMATION

Control Terminal Configuration

CDCE949

CDCEL949

SCAS844 – JUNE 2007

The CDCE949/CDCEL949 has three user-definable control terminals (S0, S1 and S2) which allow external

control of device settings. They can be programmed to perform any of the following functions:

• Spread-Spectrum Clocking selection: Spread-type and spread-amount selection

• Frequency selection: Switching between any of two user-defined frequencies

• Output-State selection: Output configuration and power-down control

The user can predefine up to eight different control settings. Table 1 and Table 2 explain these settings.

Table 1. Control Terminal Definition

External Control-Bits

PLL1 Setting

PLL2 Setting

PLL3 Setting

PLL4 Setting

Y1 Setting

Control Function

SSC Selection (Center/Down)

SSCx [3-bits]

Center

Down

0

0

0

0% (off)

0% (off)

0

0

1

±0.25%

–0.25%

0

1

0

±0.5%

–0.5%

0

1

1

±0.75%

–0.75%

1

0

0

±1.0%

–1.0%

1

0

1

±1.25%

–1.25%

1

1

0

±1.5%

–1.5%

1

1

1

±2.0%

–2.0%

FSx

FUNCTION

0

Frequency0

1

Frequency1

YxYx

FUNCTION

0

State0

1

State1

(1)

Center/Down-Spread, Frequency0/1 and State0/1 are user-definable in PLLx Configuration Register;

(2)

(3)

State0/1 selection is valid for both outputs of the corresponding PLL module and can be power down,

3-state, low or active

9

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