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VSC7173

Data Sheet

Revision 4.1

May 23, 2005

Confidential

High-Speed Outputs

Each port has a high-speed output buffer that transmits the differential serial ATA data at rates up to 3.0 Gbps. The

output pins for the ports are P0OUTP/N, P1OUTP/N, and P2OUTP/N. Each output buffer has an input to indicate

when OOB signals are being transmitted and a single input to control the output voltage amplitude and to enable pre-

emphasis.

Transmitting OOB Signals

Both differential output signals are at the DC-bias voltage when the output buffer is disabled. The output buffer is

disabled when OOB signals are transmitted and when an output port is turned “off.” For more information, see

“Functional Descriptions,” page 4.

Output Amplitude and Pre-Emphasis

Each of the output buffers has an amplitude control input pin, the state of which sets the differential output voltage

(within normal SATA levels). Pin HIV0 corresponds to port 0, pin HIV1 corresponds to port 1, and pin HIV2

corresponds to port 2. See Table 4. Recommended output AC-coupling capacitor values are 0.01

µF. When the

amplitude control pin is HIGH, the output is configured for high voltage swing mode, which is useful for driving

extended length media such as backplanes or external cables. Setting the output to high swing mode should be done

only in controlled environments, because the output voltage exceeds the Serial ATA 1.0 differential mode

specifications.

The output buffers have a pre-emphasis circuit that is enabled when HIVx is HIGH. Pre-emphasis accentuates higher

frequency signals in a transmitted data stream. This feature takes into consideration that a signal loses amplitude and

affects the data eye opening as it goes through long trace length runs. Figure 5 shows the effects of the pre-emphasis

feature. The amplitude increase is between 20% and 30%, and the duration of the amplitude increase is between

150 ps and 300 ps.

Figure 4. High-Speed Output Buffer

Table 4. Output Amplitude and Pre-Emphasis

HIVx Pin State

Output Swing Level

Pre-Emphasis

0

Normal

None

1

High

Enabled

Output

OutputN

Data

TX Common Mode

HIV