原创 cyclone 系列IO口问题--PCI clamp diode

2008-12-26 17:00 4980 10 10 分类: FPGA/CPLD
(转自)http://www.altera.com.cn/support/devices/io/features/io-features.html
1. PCI钳位二极管
到底能不能与5V接口呢?通过限流电阻R2
R1=5V设备的输出电阻,Iih是输入最大的电流,或者DIODE的最大限流
R2=(5V-3.3V)/(Iih)-R1  就是最小的限流电阻

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
    maximum level.
  • 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.


Feature Availability



  • 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.


Feature Limitations



  • 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.

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