ACEX 1K Programmable Logic Device Family Data Sheet
PCI Pull-Up Clamping Diode Option
ACEX 1K devices have a pull-up clamping diode on every I/ O, dedicated
input, and dedicated clock pin. PCI clamping diodes clamp the signal to
the VCCIO value and are required for 3.3-V PCI compliance. Clamping
diodes can also be used to limit overshoot in other systems.
Clamping diodes are controlled on a pin-by-pin basis. When VCCIO is
3.3 V, a pin that has the clamping diode option turned on can be driven by
a 2.5-V or 3.3-V signal, but not a 5.0-V signal. When VCCIO is 2.5 V, a pin
that has the clamping diode option turned on can be driven by a 2.5-V
signal, but not a 3.3-V or 5.0-V signal. Additionally, a clamping diode can
be activated for a subset of pins, which allows a device to bridge between
a 3.3-V PCI bus and a 5.0-V device.
Slew-Rate Control
The output buffer in each IOE has an adjustable output slew rate that can
be configured for low-noise or high-speed performance. A slower slew
rate reduces system noise and adds a maximum delay of 4.3 ns. The fast
slew rate should be used for speed-critical outputs in systems that are
adequately protected against noise. Designers can specify the slew rate
pin-by-pin or assign a default slew rate to all pins on a device-wide basis.
The slow slew rate setting affects only the falling edge of the output.
Open-Drain Output Option
ACEX 1K devices provide an optional open-drain output (electrically
equivalent to open-collector output) for each I/ O pin. This open-drain
output enables the device to provide system-level control signals (e.g.,
interrupt and write enable signals) that can be asserted by any of several
devices. It can also provide an additional wired-ORplane.
MultiVolt I/O Interface
The ACEX 1K device architecture supports the MultiVolt I/ O interface
feature, which allows ACEX 1K devices in all packages to interface with
systems of differing supply voltages. These devices have one set of VCC
pins for internal operation and input buffers (VCCINT), and another set for
I/ O output drivers (VCCIO).
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