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Altera Corporation
Stratix II GX Device Handbook, Volume 2
October 2007
Calibration Blocks
Termination Resistor Calibration Block
The Stratix II GX transceiver’s on-chip termination resistors in the
transceiver channels of the entire device are calibrated by a single
calibration block. This block ensures that process, voltage, and
temperature variations do not have an impact on the termination resistor
value. There is only one termination resistor calibration block per device.
The calibration block uses the reference resistor of transceiver block 0 or
transceiver block 1, depending on the device. The calibration block uses
the reference resistor in transceiver block 0 for EP2SGX30 and EP2SGX60
devices and the reference resistor in transceiver block 1 for EP2SGX90 and
EP2SGX130 devices. A reference resistor must be connected to either
transceiver block 0 or transceiver block 1 to ensure proper operation of
the calibration block, whether or not the transceiver block is in use.
Failing to connect the reference resistor of the transceiver block feeding
the calibration block results in incorrect termination values for all the
termination resistors in the transceivers of the entire device.
The termination resistor calibration circuit requires a calibration clock.
You can use a global clock line if the
REFCLK
pins are used for the
reference clock. You can instantiate a calibration clock port in the
MegaWizard to supply your own clock through the
cal_blk_clk
port.
The frequency range of the
cal_blk_clk
is 10 MHz to 125 MHz. If there
are no slow-speed clocks available, use a divide-down circuit (for
example, a ripple counter) to divide the available clock to a frequency in
that range. The quality of the calibration clock is not an issue, so PLD local
routing is sufficient to route the calibration clock.
For multiple ALT2GXB instances in the same device, if all the instances
are the same, the calibration block must be active and the
cal_blk_clk
port of all instances must be tied to a common clock. Physically, there is
one
cal_blk_clk
port per device. The Quartus II software provides an
error message if the
cal_blk_clk
port is tied to different clock sources,
because this would be impossible to fit into a device. If there are different
configurations of the ALT2GXB instance, only one must have the
calibration block instantiated. If multiple instances of the ALT2GXB
custom megafunction variation have the calibration block instantiated,
then all the
cal_blk_clk
ports must be tied to the same clock source.
The calibration block can be powered down through the optional
cal_blk_powerdown
port (this is an active low input). Powering down
the calibration block during operations may yield transmit and receive
data errors. Only use this port to reset the calibration block to initiate a
recalibration of the termination resistors to account for variations in