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Altera_Forum
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14 years ago

Terminating 3.3V LVTTL signals

AN447 seems to have conflicting statements about what outputs need to be terminated. Page 14 says "The measured current exceeds the current limit from Table 3 on page 11. In conclusion, the Cyclone driver operating at 3.3-V LVTTL with 8 mA setting is not able to drive directly to a Cyclone III and Cyclone IV device input at 3.3-V VCCIO supply without termination." Yet the current was measured at 2.4V, nowhere near the voltage at which the PCI-clamp diode starts to conduct, and the statement contradicts Table 4. Can someone explain this apparent contradiction?

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