cyclone 系列IO口问题--PCI clamp diode
When to Use
- A PCI diode-enabled pin only affects signal voltage about 0.7 V above VCCIO level. Higher voltage levels are clipped, effectively reducing voltage level at pin to about VCCIO + 0.7-V level. 0.7 V is an approximation of the on-chip diode turn-on voltage.
- Use when the voltage overshoot seen at the FPGA pin exceeds
acceptable maximum level. FPGAs in the Cyclone family have maximum DC
input and maximum overshoot (AC) voltage specifications.
- Use when interfacing a Cyclone II FPGA or a Cyclone FPGA with a
5.0-V LVTTL device to clamp voltage at the FPGA pin to an acceptable
- For all cases of usage, determine if series resistor is needed to
reduce DC current to acceptable limit through the on-chip diode.
How to Use
- In the Assignment Editor, set the PCI I/O assignment to ON to enable the on-chip clamp diode for the pin.
- All banks of user I/O pins for Cyclone III FPGAs.
- Only with side bank user I/O pins for Cyclone II and Cyclone FPGAs.
- Not supported in dedicated input clock and configuration pins.
- There is a maximum of 10-mA DC current through the on-chip clamp
diode for Cyclone III FPGAs and 25- mA for Cyclone II and Cyclone FPGAs.
- Not available in dual-purpose configuration pins that are used during configuration for FPGAs in the Cyclone III family.