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Revision 4.2

July 29, 2005

Confidential

VSC7177

Data Sheet

Inactive Port Functionality

The MODE0 pin controls the functionality of the output driver for the unconnected port.

In both edge-sensitive and level-sensitive sideband modes, the output of the unconnected port (P0OUTP/N or

P1OUTP/N) transmits port 2 input data when MODE0 is HIGH. The output driver transmits the data received by that

unconnected port when MODE0 is LOW. Note that this loopback functionality differs from the VSC7173 and the

VSC7175 in edge-sensitive sideband mode.

Table 3 summarizes the sideband-based port selection functionality.

X = don’t care;

↑ = rising.

Reset State

The power-up state of the VSC7177 while in sideband-based port selection mode is based upon the PORTSEL0 and

PORTSEL1 input signals. When in level-sensitive sideband mode, the active port connected to port 2 is controlled

directly by the PORTSEL0 input. This is the same behavior as the normal operating condition described above. When

in edge-sensitive sideband mode, the active port connected to port 2 is defined in Table 4. The state diagram in

Figure 2 indicates the same result in a different format.

Table 3. Sideband-based Port Selection Operating Modes

Input Pins

Output Pins

MODE1

MODE0

PORTSEL0

PORTSEL1

P0OUT

P1OUT

P2OUT

P0SLTD

0 (level)

0

0

P2IN

P1IN

P0IN

OOBPORT1

0 (level)

0

1

P0IN

P2IN

P1IN

OOBPORT1

0 (level)

1

0

P2IN

P2IN

P0IN

OOBPORT1

0 (level)

1

1

P2IN

P2IN

P1IN

OOBPORT1

1 (edge)

0

X

↑

P0IN

P2IN

P1IN

0

1 (edge)

0

↑

X

P2IN

P1IN

P0IN

1

1 (edge)

1

X

↑

P2IN

P2IN

P1IN

0

1 (edge)

1

↑

X

P2IN

P2IN

P0IN

1

Table 4. Power-Up State (Edge-Sensitive Sideband Mode)

PORTSEL0

PORTSEL1

Active Port

P0SLTD Output

0

0

Port 0 selected

1

1

0

Port 0 selected

1

0

1

Port 1 selected

0

1

1

Port 0 selected

1