EEPROM

Xin

Xout

VDD

GND

VDDOUT

Xtal

Y2 = 27 MHz

Y1 = 27 MHz

Y3 = 27 MHz

LV

CMOS

Pdiv1

1

=

Y4 = 27 MHz

Y5 = 27 MHz

LV

CMOS

LV

CMOS

LV

CMOS

LV

CMOS

Programming

and

SDA SCL

Register

/

Input Clock

PLL Bypass

PLL 1

Power Down

PLL Bypass

PLL 2

Power Down

S0

SDA

SCL

27-MHz

Crystal

Programming Bus

1 = Outputs Enabled

0 = Outputs Disabled

(High-Impedance)

Pdiv2

1

=

Pdiv3

1

=

Pdiv3

1

=

Pdiv4

1

=

Pdiv5

1

=

15

CDCE925, CDCEL925

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SCAS847I – JULY 2007 – REVISED OCTOBER 2016

Product Folder Links: CDCE925 CDCEL925

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Copyright © 2007–2016, Texas Instruments Incorporated

(1)

S1 is SDA and S2 is SCL in default mode or when programmed (SPICON bit 6 of register 2 set to 0). They do not have any control-pin

function but they are internally interpreted as if S1 = 0 and S2 = 0. S0, however, is a control pin which in the default mode switches all

outputs ON or OFF (as previously predefined).

Figure 7. Preconfiguration of CDCEx925 Internal EEPROM

Table 4 shows the factory default setting for the control terminal register (external control pins). Note that even

though eight different register settings are possible, in default configuration, only the first two settings (0 and 1)

can be selected with S0, as S1 and S2 are configured as programming pins in the default mode.

Table 4. Factory Default Settings for Control Terminal Register(1)

Y1

PLL1 SETTINGS

PLL2 SETTINGS

EXTERNAL CONTROL PINS

S2

S1

S0

Y1

FS1

SSC1

Y2Y3

FS2

SSC2

Y4Y5

SCL (I2C)

SDA (I2C)

0

High-

impedance

state

fVCO1_0

Off

High-

impedance

state

fVCO2_0

Off

High-

impedance

state

SCL (I2C)

SDA (I2C)

1

Enabled

fVCO1_0

Off

Enabled

fVCO2_0

Off

Enabled

9.3.3 SDA/SCL Serial Interface

This section describes the SDA/SCL interface of the CDCEx925 device. The CDCEx925 operates as a slave

device of the 2-wire serial SDA/SCL bus, compatible with the popular SMBus or I2C specification. It operates in

the standard-mode transfer (up to 100 kbps) and fast-mode transfer (up to 400 kbps) and supports 7-bit

addressing.

The SDA/S1 and SCL/S2 pins of the CDCEx925 are dual-function pins. In the default configuration they are used

as SDA/SCL serial programming interface. They can be reprogrammed as general-purpose control pins, S1 and

S2, by changing the corresponding EEPROM setting, byte 02h, bit [6].