VSC7177 查看數據表（PDF） - Maxim Integrated

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VSC7177

Enhanced 2:1 Port Selector for Serial ATA and Serial Attached SCSI

Maxim Integrated 

VSC7177

Data Sheet

Reset=1

Reset State

Reset=1

(PORTSEL0=1, PORTSEL1=1

or PORTSEL1=0)

and Reset=0

PORTSEL0=0, PORTSEL1=1

and Reset=0

Port 0 Selected

PORTSEL0

PORTSEL1

Port 1 Selected

Figure 2. Reset State Machine (Edge-Sensitive Sideband Mode)

Serial ATA II Protocol-Based Port Selection

Protocol-based port selection allows two hosts to negotiate for connection to a single device using OOB signaling.

The active host port in the VSC7177 may be selected using the protocol-based method defined in the Serial ATA II:

Port Selector 1.0 specification. Protocol-based port selection determines whether port 0 or port 1 is the active host

port connected to port 2 in this operating mode.

The Serial ATA II protocol-based port selection mode is enabled when MODE1 is LOW, MODE0 is HIGH,

PORTSEL1 is HIGH, and PORTSEL0 is LOW. Sideband-based port selection is disabled when Serial ATA II

protocol-based port selection mode is enabled.

Table 1, page 5 shows all modes of operation. This section describes how the Serial ATA II: Port Selector standard

was implemented in the VSC7177.

Neither host port (port 0 or port 1) is active following power up and reset of the VSC7177. The output buffer in the

device port (port 2) is disabled (output is at DC-bias point) when there is no active host port. Data received by the

device port is transmitted to both host ports.

The VSC7177 supports presence detection per Serial ATA II: Port Selector 1.0 specification. A six-burst COMWAKE

signal is transmitted from each host port immediately after power up. A six-burst COMWAKE signal is transmitted

from a host port each time a valid COMRESET signal is received by that host port. The VSC7177 starts transmitting

the COMWAKE signal after it has detected the COMRESET signal is no longer being received from the host. The

COMWAKE signal is transmitted in response to receiving a COMRESET signal, regardless of that port’s being active

or inactive.

When there is no active host port, the first COMWAKE or COMRESET signal received by a host port selects that port

as the active host port. A COMRESET signal is transmitted out of the device port to the device, and the now active

host port is connected to the device port. If a COMWAKE or COMRESET signal is received by both host ports

simultaneously, port 0 is given priority and is selected as the active host port.

The VSC7177 detects a port selection signal received by an inactive host port. The port selection signal is a series of

five, valid COMRESET signals. The duration between the first and second COMRESET series and the third and

fourth COMRESET series is nominally 2.0 ms. The duration between the second and third COMRESET series and

the fourth and fifth COMRESET series is nominally 8.0 ms. After the entire fifth COMRESET series has been

deasserted, the inactive port that received the port selection signal is immediately switched to be the active host port.

Figure 3 shows the port selection signal. Maintaining primitive alignment is not guaranteed. Reception of

Revision 4.2

July 29, 2005

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