EP2AGX95EF29C6N Datasheet, PDF (181/380 Pages) Altera Corporation – Device Interfaces and Integration

Chapter 6: I/O Features in Arria II Devices
I/O Structure
6–17
Bus Hold
Each Arria II device I/O pin provides an optional bus-hold feature. Bus-hold circuitry
can weakly hold the signal on an I/O pin at its last-driven state. Because the bus-hold
feature holds the last-driven state of the pin until the next input signal is present, an
external pull-up or pull-down resistor is not required to hold a signal level when the
bus is tri-stated.
Bus-hold circuitry also pulls non-driven pins away from the input threshold voltage
where noise can cause unintended high-frequency switching. You can select this
feature individually for each I/O pin. The bus-hold output drives no higher than
V_CCIO to prevent over-driving signals. If you enable the bus-hold feature, you cannot
use the programmable pull-up option. The bus-hold feature is disabled if the I/O pin
is configured for differential signals.
Bus-hold circuitry uses a resistor with a nominal resistance to weakly pull the
last-driven state and is active only after configuration. When going into user mode,
the bus-hold circuit captures the value on the pin present at the end of configuration.
f For more information about the specific sustaining current driven through this
resistor and the overdrive current used to identify the next-driven input level, refer to
Device Datasheet for Arria II Devices chapter.
Programmable Pull-Up Resistor
Each Arria II device I/O pin provides an optional programmable pull-up resistor
during user mode. If you enable this feature for an I/O pin, the pull-up resistor
weakly holds the I/O to the V_CCIO level.
Programmable pull-up resistors are only supported on user I/O pins and are not
supported on dedicated configuration pins, JTAG pins, or dedicated clock pins. If you
enable the programmable pull-up option, you cannot use the bus-hold feature.
Programmable Pre-Emphasis
Arria II LVDS transmitters support programmable pre-emphasis to compensate the
frequency dependent attenuation of the transmission line. For programmable
pre-emphasis control, the Quartus II software allows two settings for Arria II GX
devices and four settings for Arria II GZ devices.
f For more information about programmable pre-emphasis, refer to the High-Speed
Differential I/O Interfaces and DPA in Arria II Devices chapter.
Programmable Differential Output Voltage
Arria II LVDS transmitters support programmable V_OD. Programmable V_OD settings
allow you to adjust output eye height to optimize trace length and power
consumption. A higher V_OD swing improves voltage margins at the receiver end,
while a smaller V_OD swing reduces power consumption.
f For more information about programmable V_OD, refer to the High-Speed Differential I/O
Interfaces and DPA in Arria II Devices chapter.
December 2011 Altera Corporation
Arria II Device Handbook Volume 1: Device Interfaces and Integration