
IDT SerDes
PES32NT24xG2 User Manual
8 - 4
January 30, 2013
Notes
De-emphasis
The PCI Express Base Specification supports three de-emphasis levels: -3.5 dB (at 2.5 GT/s or 5.0 GT/
s speeds), -6.0 dB (only for 5.0 GT/s), and 0 dB (low-swing mode). The de-emphasis selected for the link is
controlled by the Selectable De-emphasis bit in each port’s PCI Express Link Control 2 register
1
. This field
is set by hardware or firmware (e.g., EEPROM) during boot time and remains unchanged during normal
system operation.
To allow the de-emphasis setting to be modified and customized on the link, the PES32NT24xG2
contains proprietary per-lane coarse and fine de-emphasis adjustment controls. Together, these controls
allow the nominal de-emphasis setting (i.e., -3.5 dB or -6.0 dB) to be modified with a granularity of ~0.6 dB
per setting
2
. The desired de-emphasis setting can be achieved across the range of driver level settings
described in the previous section. The PES32NT24xG2 places no restrictions on the time at which the de-
emphasis setting can be modified. Refer to section SerDes Transmitter Control Registers on page 8-6 for
details on programming the transmitter de-emphasis.
PCI Express Low-Swing Mode
PES32NT24xG2 ports support the optional low-swing transmit voltage mode defined in the PCI Express
Base Specification. In this mode, the port’s transmitter voltage level is set to approximately half the value of
the full-swing (default) mode, which results in reduced power consumption in the SerDes. In addition, signal
de-emphasis is turned off. Low-swing mode is a per-link feature, meaning that all lanes of the port operate
low-swing simultaneously. Refer to section Low-Swing Transmitter Voltage Mode on page 8-12 for details
on enabling low-swing mode on a port.
Receiver Equalization
In addition to the transmitter controls described above, the switch SerDes also contains a receiver
equalizer to compensate for effects of channel loss on received signal (i.e., high-speed signal degradation
due to the combined effects of board traces, vias, connectors, and cables in the physical link). In general,
the channel has low-pass filter characteristics, which results in the degradation of high speed signals.
Receiver equalization may be used to compensate for the lossy attenuation effects of the channel on high-
speed signals.
Receiver equalization can be controlled on a per-lane basis. Each SerDes lane contains a receiver
equalization circuit. This circuit is a multi-stage programmable amplifier, where each stage is a peaking
equalizer with a different center frequency and programmable gain. Varying amounts of gain may be
applied depending on the overall frequency response of the channel loss.
For details on programming the receiver equalizer, refer to section Receiver Equalization Controls on
page 8-14. The PES32NT24xG2 places no restrictions on the time at which the equalizer settings may be
modified (e.g., the settings can be modified during normal operation of the link or while the link is being
tested).
Programming of SerDes Controls
The SerDes controls described above may be programmed by accessing IDT proprietary registers
within the switch. The registers may be programmed via any of the mechanisms allowed by the
PES32NT24xG2 (i.e., via PCI Express configuration accesses from a root, via EEPROM loading at boot-
time, or via the switch’s SMBus slave interface). The following sections describe in detail the control regis-
ters associated with the SerDes and the manner in which the SerDes controls are programmed.
1.
In low-swing mode, de-emphasis is automatically set to 0 dB and the Selectable De-emphasis bit in the port’s
PCI Express Link Control 2 register is ignored.
2.
Note that the PCI Express Base Specification allows a deviation of +/- 0.5 dB from the nominal setting.
Содержание PCI Express 89HPES32NT24xG2
Страница 20: ...IDT Table of Contents PES32NT24xG2 User Manual x January 30 2013 Notes...
Страница 24: ...IDT List of Tables PES32NT24xG2 User Manual xiv January 30 2013 Notes...
Страница 28: ...IDT List of Figures PES32NT24xG2 User Manual xviii January 30 2013 Notes...
Страница 56: ...IDT PES32NT24xG2 Device Overview PES32NT24xG2 User Manual 1 20 January 30 2013 Notes...
Страница 100: ...IDT Switch Core PES32NT24xG2 User Manual 4 22 January 30 2013 Notes...
Страница 124: ...IDT Switch Partition and Port Configuration PES32NT24xG2 User Manual 5 24 January 30 2013 Notes...
Страница 128: ...IDT Failover PES32NT24xG2 User Manual 6 4 January 30 2013 Notes...
Страница 148: ...IDT Link Operation PES32NT24xG2 User Manual 7 20 January 30 2013 Notes...
Страница 164: ...IDT SerDes PES32NT24xG2 User Manual 8 16 January 30 2013 Notes...
Страница 170: ...IDT Power Management PES32NT24xG2 User Manual 9 6 January 30 2013 Notes...
Страница 196: ...IDT Transparent Switch Operation PES32NT24xG2 User Manual 10 26 January 30 2013 Notes...
Страница 244: ...IDT SMBus Interfaces PES32NT24xG2 User Manual 12 40 January 30 2013 Notes...
Страница 247: ...IDT General Purpose I O PES32NT24xG2 User Manual 13 3 January 30 2013 Notes...
Страница 248: ...IDT General Purpose I O PES32NT24xG2 User Manual 13 4 January 30 2013 Notes...
Страница 330: ...IDT Switch Events PES32NT24xG2 User Manual 16 6 January 30 2013 Notes...
Страница 342: ...IDT Multicast PES32NT24xG2 User Manual 17 12 January 30 2013 Notes...
Страница 344: ...IDT Temperature Sensor PES32NT24xG2 User Manual 18 2 January 30 2013 Notes...
Страница 384: ...IDT Register Organization PES32NT24xG2 User Manual 19 40 January 30 2013...
Страница 492: ...IDT Proprietary Port Specific Registers PES32NT24xG2 User Manual 21 44 January 30 2013 Notes...
Страница 588: ...IDT NT Endpoint Registers PES32NT24xG2 User Manual 22 96 January 30 2013 Notes...
Страница 710: ...IDT JTAG Boundary Scan PES32NT24xG2 User Manual 25 12 January 30 2013 Notes...
Страница 743: ...IDT Usage Models PES32NT24xG2 User Manual 26 33 January 30 2013 Notes...
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