PROASIC3E Datasheet, PDF (28/37 Pages) Actel Corporation – I/O Structures in IGLOOe and ProASIC3E Devices

I/O Structures in IGLOOe and ProASIC3E Devices
The slew rate can be implemented by using a PDC command (Table 6 on page 6), setting it "High"
or "Low" in the I/O Attribute Editor in Designer, or instantiating a special I/O macro. The default
slew rate value is "High."
IGLOOe and ProASIC3E devices support output slew rate control: high and low. Actel recommends
the high slew rate option to minimize the propagation delay. This high-speed option may
introduce noise into the system if appropriate signal integrity measures are not adopted. Selecting
a low slew rate reduces this kind of noise but adds some delays in the system. Low slew rate is
recommended when bus transients are expected.
Output Drive
The output buffers of IGLOOe and ProASIC3E devices can provide multiple drive strengths to meet
signal integrity requirements. The LVTTL and LVCMOS (except 1.2 V LVCMOS) standards have
selectable drive strengths. Other standards have a preset value.
Drive strength should also be selected according to the design requirements and noise immunity of
the system.
The output slew rate and multiple drive strength controls are available in LVTTL/LVCMOS 3.3 V,
LVCMOS 2.5 V, LVCMOS 2.5 V / 5.0 V input, LVCMOS 1.8 V, and LVCMOS 1.5 V. All other I/O
standards have a high output slew rate by default.
For other IGLOOe and ProASIC3E devices, refer to Table 15 for more information about the slew
rate and drive strength specification.
There will be a difference in timing between the Standard Plus I/O banks and the Advanced I/O
banks. Refer to the I/O timing tables in the datasheet for the standards supported by each device.
Table 15 • IGLOOe and ProASIC3E I/O Standards—Output Drive and Slew Rate
I/O Standards
2 mA 4 mA 6 mA 8 mA 12 mA 16 mA 24 mA
Slew
LVTTL/LVCMOS 3.3 V
✓
✓
✓
✓
✓
✓
✓
High Low
LVCMOS 2.5 V
✓
✓
✓
✓
✓
✓
✓
High Low
LVCMOS 2.5/5.0 V
✓
✓
✓
✓
✓
✓
✓
High Low
LVCMOS 1.8 V
✓
✓
✓
✓
✓
✓
–
High Low
LVCMOS 1.5 V
✓
✓
✓
✓
✓
–
–
High Low
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