HC4GX15 Datasheet, PDF (317/668 Pages) Altera Corporation – HardCopy IV Device Handbook

Chapter 1: HardCopy IV GX Transceiver Architecture
1–53
Transmitter Channel Datapath
transmitter buffer power supply only provides voltage to the transmitter output
buffers in the transceiver channels. The transmitter output buffer, shown in
Figure 1–41, has additional circuitry to improve signal integrity, such as V_OD,
programmable three-tap pre-emphasis circuit, internal termination circuitry, and
receiver detect capability to support PCI Express (PIPE) functional mode.
Figure 1–41. Transmitter Output Buffer
Programmable
Pre-emphasis
and V_OD
42.5Ω, 50 Ω, 60Ω, 75Ω
+VTT-
Transmitter Output Pins
42.5Ω, 50 Ω, 60Ω, 75Ω
Receiver
Detect
Programmable Transmitter Termination
The HardCopy IV GX transmitter buffer includes programmable on-chip differential
termination of 85, 100, 120, or 150 Ω . The resistance is adjusted by the on-chip
calibration circuit in the calibration block (refer to “Calibration Blocks” on
page 1–192), which compensates for temperature, voltage, and process changes. The
HardCopy IV GX transmitter buffers in the transceiver are current mode drivers.
Therefore, the resultant V_OD is a function of the transmitter termination value. For
more information about resultant V_OD values, refer to “Programmable Output
Differential Voltage” on page 1–53.
You can disable OCT and use external termination. If you select external termination,
the transmitter common mode is tri-stated. You can set the transmitter termination in
the ALTGX MegaWizard Plug-In Manager.
You can also set the OCT through the Assignment Editor. Set the assignment shown
in Table 1–9 to the transmitter serial output pin.
Table 1–9. HardCopy IV GX OCT Assignment Settings
Assign To
Transmitter Serial Output Data Pin
Assignment Name:
Available Values:
output termination
OCT 85 Ω, OCT 100 Ω, OCT 120 Ω, OCT 150 Ω
Programmable Output Differential Voltage
The HardCopy IV GX device allows you to customize the differential output voltage
to handle different trace lengths, various backplanes, and receiver requirements, as
shown in Figure 1–42. You can change the V_OD values using the dynamic
reconfiguration controller. Set the V_OD value through the tx_vodctrl[2:0] port of
the dynamic reconfiguration controller. For example, to set V_OD to a value of 3, set the
tx_vodctrl[2:0] to 011.
© June 2009 Altera Corporation
HardCopy IV Device Handbook Volume 3