IDT 89HPES12T3G2, Preliminary User'S Manual

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IDT Link Operation
PES12T3G2 User Manual 3 - 9 January 28, 2013
Notes
During normal operation (i.e, not polling.compliance), de-emphasis selection is done during the
Recovery state. The downstream component of the link (i.e., switch upstream port or endpoint) advertises
its desired de-emphasis by transmission of training sets. The upstream component of the link (i.e., switch
downstream port or root-complex port) notes its link partner desired de-emphasis, and makes a decision
about the de-emphasis to be used in the link.
The PES12T3G2’s upstream port PHY advertises its desired de-emphasis based on the setting of the
port’s SDE field in the PCIELCTL2 register. The upstream PHY always accepts the link-partners decision
on the de-emphasis to be used in the link. The PES12T3G2’s downstream ports ignore the link partner’s
desired de-emphasis, and always choose the de-emphasis setting in the SDE field of the port’s PCIELCTL2
register.
Low-Swing Transmitter Voltage Mode
The PES12T3G2 ports support the optional low-swing transmit voltage mode defined in the PCIe 2.0
specification. In this mode, the transmitter’s voltage level is set to approximately half the value of the full-
swing (default) mode. This reduces power consumption in the SerDes. This mode is enabled by setting the
Low-Swing Enable (LSE) bit in the port’s SerDes Control (SERDESCTL) register.
When Low-Swing mode is enabled, the transmitter drive level is reduced and de-emphasis is automati-
cally turned off. Therefore, the Selectable De-emphasis (SDE) and Compliance De-emphasis (CDE) fields
in the PCIELCTL2 register have no effect. Additionally, the Current De-emphasis (CDE) field in the
PCIELSTS2 register becomes invalid.