> Omer YALHI wrote:
>> I am going to be interfacing the PIC with LTC1257.  The PIC will be
>> powered by ~3.3V and the LTC1257 needs 5V.  It is easy to supply the
>> 5V; however, will I need a level translator or will the LTC1257 work
>> without one?  I searched DigiKey for Maxim level translators (or any
>> level translator for that matter) and none found except for a level
>> translator for a SIM card, LTC1555.
>
> No, I'm not going to look up what a LTC1257 is just to answer a PIClist
> question.
>
> A cheap trick for level translating from 3.3V to 5V is using digital logic
> gates with TTL inputs powered at 5V.  However, this only works in one
> direction.
>

Looking at the datasheet for the LTC1257, Vih is 2.4V minimum so if the PIC 
can drive its pins to at least 2.4V you should be fine driving Din, CLK and 
LOAD- from the PIC.  I haven't looked at a 3.3V PIC in a while but I seem to 
remember it drove output pins very nicely, nearly full rail-to-rail.  Check 
that a low output is below 0.8V so the LTC1257 also recognizes it as low.

If you are wanting to monitor Dout from the LTC1257 (not sure why you would) 
then you could just use a series resistor to limit current into the PIC's 
input clamps.  Again, according to the LTC1257 data sheet Voh is a minimum 
of Vcc-1 and 1mA.  Maximum would of course be Vcc.  If you don't like that 
idea, just make yourself a little voltage divider or use a NPN or FET 
switched by Dout and jerking the PIC's input pin from 0V to 3.3V.  If the 
data rate is too high, these tricks don't work very well.

Now I am ready to be flamed by all those that think the PIC's I/O pins can't 
handle this...

Rob Young
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