6–6
Chapter 6: I/O Features in the Cyclone III Device Family
I/O Element Features
asynchronous preset can control the registers. This feature prevents the inadvertent
activation of the active-low input of another device upon power up. If one register in
an IOE uses a preset or clear signal, all registers in the IOE must use that same signal if
they require preset or clear. Additionally, a synchronous reset signal is available for
the IOE registers.
f
For more information about the input and output pin delay settings, refer to the Area
and Timing Optimization chapter in volume 2 of the Quartus II Handbook.
PCI-Clamp Diode
The Cyclone III device family provides an optional PCI-clamp diode enabled input
and output for each I/O pin. Dual-purpose configuration pins support the diode in
user mode if the specific pins are not used as configuration pins for the selected
configuration scheme. For example, if you are using the active serial (AS)
configuration scheme, you cannot use the clamp diode on the ASDOand nCSOpins in
user mode. Dedicated configuration pins do not support the on-chip diode.
The PCI-clamp diode is available for the following I/O standards:
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■
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3.3-V LVTTL
3.3-V LVCMOS
3.0-V LVTTL
3.0-V LVCMOS
2.5-V LVTTL/LVCMOS
PCI
PCI-X
If the input I/O standard is 3.3-V LVTTL, 3.3-V LVCMOS, 3.0-V LVTTL,
3.0-V LVCMOS, 2.5-V LVTTL/LVCMOS, PCI, or PCI-X, the PCI clamp diode is
enabled by default in the Quartus II software.
f
For more information about the Cyclone III device family PCI-clamp diode support,
refer to AN 447: Interfacing Cyclone III and Cyclone IV Devices with 3.3/3.0/2.5-V
LVTTL/LVCMOS I/O Systems.
LVDS Transmitter Programmable Pre-Emphasis
The Cyclone III device family true LVDS transmitter supports programmable
pre-emphasis. Programmable pre-emphasis is used to compensate the
frequency-dependent attenuation of the transmission line. It increases the amplitude
of the high-frequency components of the output signal, which cancels out much of the
high-frequency loss of the transmission line.
The Quartus II software allows two settings for programmable pre-emphasis
control—0 and 1, in which 0 is pre-emphasis off and 1 is pre-emphasis on. The default
setting is 1. The amount of pre-emphasis needed depends on the amplification of the
high-frequency components along the transmission line. You must adjust the setting
to suit your designs, as pre-emphasis decreases the amplitude of the low-frequency
component of the output signal as well.
Cyclone III Device Handbook
Volume 1
July 2012 Altera Corporation
ALTERA [ ALTERA CORPORATION ]
