Altera Corporation
2–51
October 2007
Stratix II GX Device Handbook, Volume 2
Stratix II GX Transceiver Architecture Overview
drivers, so the resultant V
OD
is a function of the transmitter termination
value. Refer to
“Programmable Voltage Output Differential (VOD)” on
page 2–48
for more information regarding resultant V
OD
values. You can
disable the on-chip termination to use external termination. If you select
external termination, the transmitter common mode is also tri-stated.
You select transmitter termination in the Quartus II software (in the
Assignments menu choose Assignment Organizer, then Options for
Individual Nodes Only, and then Stratix II GX Termination Value). By
default, the value is 100
Ω
. If you plan to use 100-
Ω
termination, the
Quartus II software automatically sets it during the compilation.
You set the transmitter termination setting through a pull-down menu in
the ALT2GXB MegaWizard
Programmable Common Mode
You can set the common mode in Stratix II GX devices to 600 mV or
700 mV. Use the 600-mV setting with the 1.2-V PCML standard. Use the
700-mV setting for the 1.5-V PCML standard.
Table 2–9
shows the
available common mode settings for 1.2-V/1.5-V V
CCH
.
PCI Express Receiver Detect
The Stratix II GX transmitter buffer has a built-in receiver detection
circuit for use in the PIPE mode. This circuit detects if there is a receiver
downstream by sending out a pulse on the common mode of the
transmitter and monitoring the reflection. This mode requires the
transmitter buffer to be tri-stated (in Electrical Idle mode) and the use of
on-chip termination and a 125 MHz
fixedclk
signal.
Table 2–9. Common Mode Settings for the Available PCML Standards
Note (1)
Common Mode Settings
1.2-V PCML Standard
1.5-V PCML Standard
Data Rates (Mbps)
600 mV
v
v
600 to 3125
600 mV
—
v
3126 to 6375
700 mV
—
v
600 to 3125
Note to
Table 2–9
:
(1)
The PIPE protocol only allows 1.2-V PCML with 600 mV common mode. It does not allow a 1.5-V PCML and
700 mV combination.