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Revision 4.2

July 29, 2005

Confidential

VSC7177

Data Sheet

COMRESET signals by an active host port are transmitted out of the device port even if the COMRESET signals are

a valid port selection signal. Refer to the Serial ATA II: Port Selector Revision 1.0 specification for a complete

definition of the port selection signals.

In the situation where a port selection signal is received when neither port is active (following a reset condition, for

example), the port receiving the signal becomes the active host port based on the first COMRESET series. All five

series of COMRESET signals are transmitted from the device port. A COMRESET signal is sent to the device in

response to the first COMRESET series and makes that port active. The remaining four series of COMRESET signals

are transmitted to the device because OOB signals are always transmitted once a host port has been connected to the

device port.

A COMRESET signal transmitted to a device causes the device to respond with a COMINIT signal. To prevent this

COMINIT signal from being squelched by the presence detection circuit’s COMWAKE transmission, the VSC7177

continuously transmits a COMRESET pattern to the device until the COMWAKE transmission is completed. This

guarantees the COMINIT signal from the device is propagated to the host.

Only OOB signals from an active host port are propagated to the device port. OOB signals from an inactive host port

are not propagated to the device port. If no active host port is selected, OOB signals received by the device port are

propagated to both host ports. When an active host port exists, OOB signals received by the device port are

propagated only to the active host port.

Data is transferred between the host and device ports without the use of PHYs. Power management, speed

negotiation, and spread spectrum clocking is indirectly supported by VSC7177 because data is merely passed through

the device.

Figure 3. Port Selection Signal

Valid COMSET Signals

Inter-reset

Assertion Delay

Minimum

Typical

Maximum

Unit

1.6

2.0

2.4

ms

7.6

8.0

8.4

ms