Chapter 6: I/O Features in the Cyclone III Device Family
I/O Element Features
Programmable Pull-Up Resistor
Each Cyclone III device family I/O pin provides an optional programmable pull-up
resistor while in user mode. If you enable this feature for an I/O pin, the pull-up
resistor holds the output to the V
level of the output pin’s bank.
If you enable the programmable pull-up, the device cannot use the bus-hold feature.
Programmable pull-up resistors are not supported on the dedicated configuration,
JTAG, and dedicated clock pins.
When the optional
signal drives low, all I/O pins remain tri-stated even if the
programmable pull-up option is enabled.
The Cyclone III device family IOE includes programmable delays to ensure zero hold
times, minimize setup times, increase clock-to-output times, or delay the clock input
A path in which a pin directly drives a register may require a programmable delay to
ensure zero hold time, whereas a path in which a pin drives a register through
combinational logic may not require the delay. Programmable delays minimize setup
time. The Quartus II Compiler can program these delays to automatically minimize
setup time while providing a zero hold time. Programmable delays can increase the
register-to-pin delays for output registers. Each dual-purpose clock input pin
provides a programmable delay to the global clock networks.
lists the programmable delays for the Cyclone III device family.
Table 6–2. Cyclone III Device Family Programmable Delay Chain
Input pin-to-logic array delay
Input pin-to-input register delay
Output pin delay
Dual-purpose clock input pin
Quartus II Logic Option
Input delay from pin to internal cells
Input delay from pin to input register
Delay from output register to output pin
Input delay from dual-purpose clock pin to fan-out destinations
There are two paths in the IOE for an input to reach the logic array. Each of the two
paths can have a different delay. This allows you to adjust delays from the pin to the
internal logic element (LE) registers that reside in two different areas of the device.
You must set the two combinational input delays with the input delay from pin to
internal cells logic option in the Quartus II software for each path. If the pin uses the
input register, one of the delays is disregarded and the delay is set with the input
delay from pin to input register logic option in the Quartus II software.
The IOE registers in each I/O block share the same source for the preset or clear
features. You can program preset or clear for each individual IOE, but you cannot use
both features simultaneously. You can also program the registers to power-up high or
low after configuration is complete. If programmed to power-up low, an
asynchronous clear can control the registers. If programmed to power-up high, an
Cyclone III Device Handbook
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