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Revision 4.2

July 29, 2005

Confidential

VSC7177

Data Sheet

Pinout Differences Between VSC7177 and VSC7173/VSC7175

The VSC7177 device is an upgrade to the VSC7173 and the VSC7175 devices. The VSC7177 package is the same as

the VSC7173 and the VSC7175; however, there are two pin requirement changes to be aware of when using a

VSC7177 device on a board designed for the VSC7173 or the VSC7175.

●

Pin 25 (VDDN) in the VSC7177 is an internally-generated 1.8 V supply voltage. This pin must be connected

to a capacitor as described in “Voltage Regulator,” page 12. Pin 25 (Reserved) is not used in the VSC7173 or

in the VSC7175.

●

Pin 18 (PORTSEL1) and pin 21 (MODE1) in the VSC7177 must both be set LOW to enable level-sensitive

sideband mode. Setting PORTSEL1 HIGH enables the protocol-based port selection mode listed in Table 1,

page 5. In the VSC7173 and the VSC7175, setting only pin 21 (MODE1) to LOW is required to enable

level-sensitive sideband mode. Pin 18 (HSTSELB) in the VSC7173 and the VSC7175 is not used in the this

mode and is a “don’t care” (connect to any value). The logical value of PORTSEL0/HSTSELA (pin 19 in the

VSC7177, the VSC7173, and the VSC7175) selects the connected port in level-sensitive mode.

●

Pin 9 in the VSC7175 (OOBDTA) reports the OOB status for Host A. For the VSC7177 device, pin 9

(OOBPORT0) reports the OOB status for the unselected host port.

Table 8 provides a summary of the pinout differences.

Sideband Loopback Function

A sideband loopback feature has been added to the VSC7177 in sideband mode. Consequently, the VSC7177 has

different functionality than either the VSC7173 or the VSC7175 in this mode. Port 2 can be connected to port 0 or

port 1 in sideband mode. The data transmitted from the output driver of the unconnected port can be data from port 2

(the downstream device) or data from the unconnected port’s input receiver (loopback data). The data transmitted is

selected with the MODE0 input. The ability to loopback the data from the unconnected port is a new feature for

sideband mode. Both the VSC7173 and the VSC7175 transmit the downstream device data or a common-mode signal

from the unconnected port’s output driver. The VSC7177 cannot directly force transmission of common mode from

the unconnected port. Transmission of common mode is achieved indirectly by enabling the loopback mode and

having the host send a common mode signal to the VSC7177.

Table 8. VSC7177 and VSC7173/VSC7175 Pinout Differences

Pin

Number

Operating Mode

Pin Function / Connectivity

VSC7173

VSC7175

VSC7177

18

Level-sensitive

sideband mode

X (don’t care)

X (don’t care)

VSS (ground)

25

All modes

Not used

Not used

Connect to external capacitor

9

All modes

OOB status for Port 0

OOB status for Host A

OOB status for unselected host port