VSC7173
Datasheet
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.
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Output
Data
OutputN
HIV
TX Common Mode
Figure 4. High-Speed Output Buffer
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
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
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.
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.
Table 4. Output Amplitude and Pre-Emphasis
HIVx Pin State
0
1
Output Swing Level
Normal
High
Pre-Emphasis
None
Enabled
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VMDS-10121 Revision 4.1
May 23, 2005
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