PROASIC3E Datasheet, PDF (15/37 Pages) Actel Corporation – I/O Structures in IGLOOe and ProASIC3E Devices

I/O Structures in IGLOOe and Pro ASIC3E Devices
I/O Features
Low-power flash devices support multiple I/O features that make board design easier. For example,
an I/O feature like Schmitt Trigger in the ProASIC3E input buffer saves the board space that would
be used by an external Schmitt trigger for a slow or noisy input signal. These features are also
programmable for each I/O, which in turn gives flexibility in interfacing with other components.
The following is a detailed description of all available features in low-power flash devices.
I/O Programmable Features
Low-power flash devices offer many flexible I/O features to support a wide variety of board
designs. Some of the features are programmable, with a range for selection. Table 8 lists
programmable I/O features and their ranges.
Table 8 • Programmable I/O Features (user control via I/O Attribute Editor)
Feature
Description
Range
Slew Control
Output slew rate
HIGH, LOW
Output Drive (mA)
Output drive strength
2, 4, 6, 8, 12, 16, 24
Skew Control
Output tristate enable delay option
ON, OFF
Resistor Pull
Resistor pull circuit
Up, Down, None
Input Delay
Input delay
OFF, 0–7
Schmitt Trigger
Schmitt trigger for input only
ON, OFF
Note: Limitations of these features with respect to different devices are discussed in later sections.
Hot-Swap Support
A pull-up clamp diode must not be present in the I/O circuitry if the hot-swap feature is used. The
3.3 V PCI standard requires a pull-up clamp diode on the I/O, so it cannot be selected if hot-swap
capability is required. The A3P030 device does not support 3.3 V PCI, so it is the only device in the
ProASIC3 family that supports the hot-swap feature. All devices in the ProASIC3E family are hot-
swappable. All standards except LVCMOS 2.5/5.0 V and 3.3 V PCI/PCI-X support the hot-swap
feature.
The hot-swap feature appears as a read-only check box in the I/O Attribute Editor that shows
whether an I/O is hot-swappable or not. Refer to Power-Up/-Down Behavior of Low-Power Flash
Devices for details on hot-swapping.
Hot-swapping (also called hot-plugging) is the operation of hot insertion or hot removal of a card
in a powered-up system. The levels of hot-swap support and examples of related applications are
described in Table 9 on page 16 to Table 12 on page 17. The I/Os also need to be configured in hot-
insertion mode if hot-plugging compliance is required. The AGL030 and A3P030 devices have an I/O
structure that allows the support of Level 3 and Level 4 hot-swap with only two levels of staging.
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