[SOLVED] Interfacing ADC ICL7135 with nexys 2

[rajanb89]

I want to interface ICL 7135 ADC with nexys 2 kit provided by digilent. How to do that??
it contains PMOD connectors. i think that might be helpful, i just want to know, where to connect my adc.

 

[FvM]

There are "tons" of ADCs better suited for FPGA interface than ICL7135, but it can be done.

You'll need 5V to 3.3V level converters, and decoding the multiplexed BCD outputs. All accessible IO pins at NEXYS 2 are interfaced through the Hirose FX2 connector, I think.

 

[mrflibble]

You can use the PMOD connectors for this, no need for the FX2 connector. The FX2 connector is mostly for when you 1) need even more pins or 2) better quality signals for some higher speeds.

And you do indeed need level translation between 5.0 and 3.3 volt, because that spartan-3E is NOT properly 5 Volt tolerant.

However if you are feeling up to it and/or the logic level converter shop is closed, you can use a fairly large series resistor to limit current and then let the clamping diodes do some clamping. This is not "the way is should be done", but I've done this plenty of times on the nexys2 and it works just fine for slow speed inputs. But if you want to do this you really should read the IBIS data for the spartan-3E to be sure you know what you're doing. Since this thing is probably going to be pretty slow I'd use something like 4.7K or even 10K. Oh yeah, and when you do that, please make sure that the IO voltage for that bank is 3.3 Volt (and not 2.5 Volt or something ).

But again ... the safe option is to use a level converter, they are dirt cheap so that should be no issue.

 

[rajanb89]

Thanks, I think i will get it done now