C.3 diode to V+ necessary?

premelec

Senior Member
SERIN notes that there is no clamp diode from C.3 input to V+ - is this only required when input is from different V+ power supplied source than PICAXE V+ ?
 

PhilHornby

Senior Member
I think you're right - it's presumably for if you're connecting to an olde-worlde RS232C interface, with its 'wild' (non-Picaxe friendly) voltages.

Having failed to read that part of the manual, I didn't know it was "required for it work", so I've never connected any such diode :)
 

premelec

Senior Member
Thanks PhilH -I'm about to find out if it's required ;-0 One more possible fail point in complicated setup...
 

inglewoodpete

Senior Member
Correct. The external protection diode is only required, in combination with a current limiting resistor, when an external input source has a potential greater than the PIC's supply rail + ~0.6v. And, of course, it is not necessarily pin C.3 but the base PIC's Reset/Vpp pin (18M2, 20M2 and 20X2).
 
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