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DE2 5Volt input to GPIO pins

Altera_Forum
Honored Contributor II
‎04-17-2009 04:49 AM
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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 of my card reader are set to 400mV and not 5V idle levles.  

 

I have tried using a 3.3V Zener Diode to bring my voltage down for the FPGA but the same problem happens. Can you help me? :confused:
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Altera_Forum
Honored Contributor II
‎04-17-2009 06:32 AM
202 Views

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.
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