VSC8504-02 datasheet(29/131 Pages) MICROSEMI

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Functional Descriptions

VMDS-10507 VSC8504-02 Datasheet Revision 4.2

media link established. The following table shows the possible link conditions based on preference

settings.

The status of the media mode selected by the AMS can be read from device register 20E1, bits 7:6. It

indicates whether copper media, SerDes media, or no media is selected. Each PHY has four automatic

media sense modes. The difference between the modes is based on the SerDes media modes:

•

SGMII or QSGMII MAC to AMS and 1000BASE-X SerDes

•

SGMII or QSGMII MAC to AMS and 100BASE-FX SerDes

•

SGMII or QSGMII MAC to AMS and SGMII (protocol transfer)

For more information about SerDes media mode functionality with AMS enabled, see SerDes Media

Interface, page 13.

3.7

Reference Clock

The device reference clock supports both 25 MHz and 125 MHz clock signals. The reference clock can

be either differential or single-ended. If differential, it must be capacitively coupled and LVDS compatible.

3.7.1

Configuring the Reference Clock

The REFCLK_SEL2 pin configures the reference clock speed. The following table shows the functionality

and associated reference clock frequency.

3.7.2

Single-Ended REFCLK Input

To use a single-ended reference clock, an external resistor network is required. The purpose of the

network is to limit the amplitude and to adjust the center of the swing. The configurations for a single-

ended REFCLK, with the clock centered at 1 V and a 500 mV peak-to-peak swing, are shown in the

following illustrations.

Figure 20 •

2.5 V CMOS Single-Ended REFCLK Input Resistor Network

Table 4 •

AMS Media Preferences

Preference

Setting

Cat5 Linked,

Fiber Not Linked

SerDes Linked,

Cat5 Not Linked

Cat5 Linked,

SerDes Attempts

to Link

SerDes Linked,

Cat5 Attempts

to Link

Both Cat5 and

SerDes Attempt

to Link

SerDes

Cat5

SerDes

Cat5

SerDes

Cat5

Table 5 •

REFCLK Frequency Selection

REFCLK_SEL2 Frequency

025 MHz

1125 MHz

DD1A

SSA

DD1A

REFCLK_P

REFCLK_N

220

910

2.5 V

CMOS

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