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Revision 4.2

July 29, 2005

Confidential

VSC7177

Data Sheet

Modes of Operation

The VSC7177 has two modes of operation: sideband port selection and protocol port selection. Each mode

corresponds to a different method of configuring port connectivity. Only one of the operating modes is active at any

time in the VSC7177. Sideband-based port connectivity is controlled externally using the I/O pins of the device itself.

Protocol-based connectivity is implemented as defined in the Serial ATA II: Port Selector 1.0 specification.

Selecting Operating Modes

There are two types of sideband-based port selections: Edge-sensitive and level-sensitive. Rising-edge transitions on

the PORTSEL0 and PORTSEL1 inputs cause the corresponding port to become active when in edge-sensitive

sideband-based selection mode. Edge-sensitive sideband port selection is enabled when MODE1 is HIGH.

PORTSEL0 determines the active port in level-sensitive sideband-based mode. Level-sensitive sideband port

selection is enabled when MODE1 is LOW and PORTSEL1 is LOW.

Setting MODE1 LOW and PORTSEL1 HIGH in the VSC7177 allows the protocol-based Serial ATA II port selection

and test modes to be enabled. PORTSEL0 and MODE0 are used to select these operating modes shown in Table 1.

The functionality of the various operating modes is described in the following sections.

The setting of PORTSEL1 constitutes one of the primary differences between the VSC7177 and the VSC7173 and the

VSC7175. In the VSC7177, PORTSEL1 must be set LOW in level-sensitive sideband mode. The setting of

PORTSEL1 has no effect on the operation of the VSC7173 and the VSC7175 in level-sensitive mode (it is a “don’t

care”). For a complete list of differences between the VSC7177 and the VSC7173 and the VSC7175, see “Pinout

Differences Between VSC7177 and VSC7173/VSC7175,” page 13.

Table 1 shows how to configure the VSC7177 to operate in any of the various available modes.

X = don’t care;

↑ = rising.

PORTSEL1 = X.)

Table 1. Operating Modes

Modes of Operation

Configuration Pins

MODE1

MODE0

PORTSEL0

PORTSEL1

Edge-sensitive sideband port selection

1

Select output mode of

unconnected port

↑ edge makes port 0

active

↑ edge makes port 1

active

Level-sensitive sideband port selection

0

Select output mode of

unconnected port

Selects connected port

Reserved

0

0

0

1

Test modes

0

0

1

1

Protocol-based Serial ATA II port

selection

01

0

1

Test modes

0

1

1

1