EP3C80 datasheet(104/274 Pages) ALTERA

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6–6

Chapter 6: I/O Features in the Cyclone III Device Family

I/O Element Features

Cyclone III Device Handbook

July 2012

Altera Corporation

Volume 1

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 ASDO and nCSO pins 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:

■

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.

EP3C80 Datasheet(PDF) 104 Page - Altera Corporation

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