EEPROM

Xin

Xout

GND

Vddout

X-tal

Y2=27MHz

Y1=27MHz

Y3=27MHz

LV

CMOS

Pdiv1 =1

Y4=27MHz

Y5=27MHz

Y6=27MHz

Y7=27MHz

LV

CMOS

Pdiv7=1

Pdiv6=1

LV

CMOS

LV

CMOS

Pdiv5=1

Pdiv4=1

LV

CMOS

LV

CMOS

Pdiv3=1

Pdiv2=1

LV

CMOS

Programming

and

SDA/SCA

Register

InputClock

PLL Bypass

PLL1

powerdown

PLL Bypass

PLL 2

powerdown

PLL Bypass

PLL3

powerdown

S0

SDA

SCL

27 MHz

Crystal

ProgrammingBus

“1” = outputsenabled

“0” =outputs3-State

CDCE937-Q1

CDCEL937-Q1

www.ti.com

SCAS892B – FEBRUARY 2010 – REVISED MAY 2010

S1/SDA and S2/SCL pins of the CDCE937/CDCEL937 are dual function pins. In default configuration they are

defined as SDA/SCL for the serial interface. They can be programmed as control-pins (S1/S2) by setting the

relevant bits in the EEPROM. Note that the changes to the Control register (Bit [6] of Byte [02]) have no effect

until they are written into the EEPROM.

forced to GND, the two control-pins, S1 and S2, temporally act as serial programming pins (SDA/SCL).

S0 is not a multi-use pin, it is a control pin only.

DEFAULT DEVICE SETTING

The internal EEPROM of CDCE937/CDCEL937 is preconfigured as shown in Figure 6. (The input frequency is

passed through to the output as a default). This allows the device to operate in default mode without the extra

production step of program it. The default setting appears after power is supplied or after power-down/up

sequence until it is re-programmed by the user to a different application configuration. A new register setting is

programmed via the serial SDA/SCL Interface.

Figure 6. Default Device Setting

Table 4 shows the factory default setting for the Control Terminal Register (external control pins). In normal

operation, all 8 register settings are available, but in the default configuration only the first two settings (0 and 1)

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

Y1

PLL1 Settings

PLL2 Settings

PLL3 Settings

Frequenc

Frequenc

Output

Frequency

SSC

Output

SSC

Output

SSC

Output

External Control Pins

y

y

Selection

Selection

Selection

Selection

Selection

Selection

Selection

Selection

Selection

Selection

S2

S1

S0

Y1

FS1

SSC1

Y2Y3

FS2

SSC2

Y4Y5

FS3

SSC3

Y6Y7

SCL (I2C)

SDA (I2C)

0

3-state

off

3-state

off

3-state

off

3-state

SCL (I2C)

SDA (I2C)

1

enabled

off

enabled

off

enabled

off

enabled

(1)

In default mode or when programmed respectively, S1 and S2 act as serial programming interface, SDA/SCL. 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).

Copyright © 2010, Texas Instruments Incorporated

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Product Folder Link(s): CDCE937-Q1