>>>Being a digital input on the PIC, it shouldn't make a difference
>>>whether it is a generic input pin or an I2C input. Therefore, you
>>>would just look at the electrical characteristics charts at the end of
>>>the datasheet to find the min/max voltage thresholds for a digital
>>>input pin.
>>
>> But I believe the SMBus levels assume the use of 3V3 logic, so have lower
>> threshold levels than 'normal' 5V I2C levels (and this would be borne out 
>> by
>> the OPs quoted levels). I believe this is why the extra function is 
>> added.
>> It may not appear on 3V3 only PICs, I haven't checked.
>>
>
> Page 347 of the datasheet says that, with SMBus enabled, the
> thresholds are 0.8/2.1v.
>
> --
> Martin K.

Ah, thanks Martin. I hadn't realised Microchip had just updated the 18f2321 
datsheet - that info wasn't in the previous one I only saved recently. 

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