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发表于 2009-10-31 13:44:08
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官方讲了5V和3.3V如何驱动,
意思是5->>3.3时,接限流电阻
3.3->>5TTL,直接接;
3.3->>5.5CMOS,设置为开漏模式并加外部上拉电阻到5V。但要注意端口保护。
原文如下:
Because MAX II devices are 3.3-V, 32-bit, 66-MHz PCI compliant, the input circuitry accepts a maximum high-level input voltage (VIH) of 4.0 V. To drive a MAX II device with a 5.0-V device, you must connect a resistor (R2) between the MAX II device and the 5.0-V device.
A MAX II device can drive a 5.0-V TTL device by connecting the VCCIO pins of the MAX II device to 3.3 V.
To make MAX II device outputs compatible with 5.0-V CMOS devices, configure the output pins as open-drain pins with the I/O clamp
diode enabled, and use an external pull-up resistor.
The purpose of enabling the I/O clamp diode is to protect the MAX II device’s I/O pins.
The I/O clamp diode is only supported in the EPM1270 and EPM2210 devices’ I/O Bank 3. An external protection diode is needed for other I/O banks in EPM1270 and EPM2210 devices and all I/O pins in EPM240 and EPM570 devices. |
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