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Altera_Forum's avatar
Altera_Forum
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17 years ago

DE2 5Volt input to GPIO pins

Hi, I am a student at OIT and i am using the Terasic DE2 development board. I have a 5V TTL serial card reader that I would like to interface to my board. But every time I plug it in the outputs o...
Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
17 years ago

DE2 has clamp diodes and series resistors and thus (limited) TTL compatibility at the GPIO inputs. For slow and medium speed signals, additional series resistors would be meaningful to reduce the input currents. The 3.3V output level can drive TTL with no additional hardware. 5V CMOS inputs need level shifters to achieve a specified minimum high level of 3.5V.

Thus it seem to be a problem of the connected hardware rather than DE2.