I have a serious problem. PIC16F54-I/P with 3.58 MHz CF and internal caps, 5V
supply. The chip does not come out of reset and stops working as soon as any pin
configured as input is pulled to -0.7V or so (via a resistor, i.e. making use of
the 'inherent' internal clamp diode). Removing the negative voltage starts the
chip. Note that only a Schottky diode brings relief, a normal 1N4148 has too
much Vf !

The datasheet [1] specifies +/-20mA clamp current on any pin except TOCKI and
-0.6V..VDD+0.6V on any pin. My injected current is about -7mA (1k to -8.2V). How
do I interpret the datasheet wrt 'clamp current' in this context ?!

[1] "PIC16F5X Data Sheet" (DS41213C), PDF document
Page 61, "11.0 ELECTRICAL SPECIFICATIONS FOR PIC16F54/57", "Voltage on all other
pins with respect to VSS ... -0.6V to (VDD + 0.6V)", "Input clamp current, IIK
(VI < 0 or VI > VDD) ... 20 mA"

Imho the clamp current specification (input *AND* output, no less) is useless
and wrong (and dangerous - I have to modify my board). I would expect the maker
to test such things from time to time and issue a datasheet errata. In the past
this has happened to PICs with A/D where the voltage on any input is now given
as +/-0.3V and the same clamp current data (+/-20mA) is given (how come ?! - eg.
PIC16F62X datasheet - 17.0 electrical specs). Why do *I* have to find these
things ?

Any comments are welcome.

Peter


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