I/O Structures in IGLOO and Pro ASIC3 Devices
v1.1
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"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."
IGLOO and ProASIC3 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 IGLOO and ProASIC3 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 30 k gate devices, refer to
Table 7-14. For other ProASIC3 and IGLOO devices, refer to
Table 7-15There 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 7-14 IGLOO and ProASIC3 Output Drive and Slew for Standard I/O Bank Type (for 30 k gate devices)
I/O Standards
2 mA
4 mA
6 mA
8 mA
Slew
LVTTL/LVCMOS 3.3 V
High
Low
LVCMOS 2.5 V
High
Low
LVCMOS 1.8 V
–
High
Low
LVCMOS 1.5 V
––
–
High
Low
Table 7-15 IGLOO and ProASIC3 Output Drive and Slew for Standard Plus I/O Bank Type
I/O Standards
2 mA
4 mA
6 mA
8 mA
12 mA
16 mA
Slew
LVTTL
High
Low
LVCMOS 3.3 V
High
Low
LVCMOS 2.5 V
*
*
–High
Low
LVCMOS 1.8 V
–
High
Low
LVCMOS 1.5 V
–
–––
High
Low
Note: *Not available in Automotive devices.