VSC8504-02 datasheet(127/131 Pages) MICROSEMI

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Design Considerations

VMDS-10507 VSC8504-02 Datasheet Revision 4.2

116

Design Considerations

This section provides information about design considerations for the VSC8504-02 device.

8.1

Link status LED remains on while COMA_MODE pin is

asserted high

When the COMA_MODE is asserted high, the link status LED may not deactivate unless the media cable

is disconnected from the device.

While using COMA_MODE, link status should be verified using status registers rather than LED

indicators.

8.2

LED pulse stretch enable turns off LED pins

Enabling the pulse stretch function for LED0 or LED1 by setting register 30, bits 5:6 shuts off those LED

pins.

Use the default blink function setting of LED0 and LED1 rather than pulse stretching. For more

information, see LED Behavior, page 60.

8.3

AMS and 100BASE-FX

When the PHY operating mode (set in register 23) is AMS and the current active media is 100BASE-FX,

forced mode. But in this mode, it has other meanings.

The workaround is to ensure that bit 12 is always written as 1 when doing writes or updates to register 0

in AMS mode.

8.4

10BASE-T signal amplitude

10BASE-T signal amplitude can be lower than the minimum specified in IEEE 802.3 paragraph

14.3.1.2.1 (2.2 V) at low supply voltages.

This issue is not estimated to present any system level impact. Performance is not impaired with cables

up to 130 m with various link partners.

8.5

10BASE-T link recovery failures

If the link disconnects when traffic is flowing while the device operates in a 10BASE-T mode, the PHY

may not re-link.

There is a software workaround for this issue in which the device's internal microcontroller monitors link

transitions in 10BASE-T mode and forces a soft power-down/power-up procedure to prevent a re-link

failure.

A side effect of this software workaround is that non-sticky registers will be cleared (for example, the

copper media link disconnect counter in register 21, see Error Counter 3, page 54).

8.6

SNR degradation and link drops

The link may drop after approximately 100 master/slave relationship swaps with the ring resiliency

feature when using Category 5 (Cat5) cables that are longer than 75 m.

The workaround is to use a combination of an initialization script and a procedure change. Contact

Microsemi for the workaround solution if the ring resiliency feature is being enabled.

8.7

Clause 45 register 3.22

The clause 45, register 3.22 is cleared upon read only when the extended page access register (register

31) is set to 0.

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