On Thu, 8 Apr 1999 16:50:23 -0400 Howard McGinnis writes: >Can an overvoltage condition on the analog input cause the processor >to >head for left field? Yes it sure can. It is possible to get into states that WDT or even MCLR can't recover from. At the very least, connect a resistor in series from the external wiring to the PIC inputs. Microchip recommends driving the analog inputs with an impedance of 10K or less, so the resistor should be 10K or less. Digital inputs can use larger resistors, though very large ones will slow down the response time. The resistor will limit the current that flows into the PIC pin when the input voltage is excessive. A simple series resistor is probably enough to deal with your situation. More complicated protection networks can give better protection when the overvoltages are high. The more complicated network is typically a "T" with 2 resistors in series with the signal path and some sort of voltage clamping device from the center of the T to ground. Resetting the WDT during a timer interrupt doesn't use it to maximum advantage. It is quite possible for the main program to get lost but the interrupts continue to function. ___________________________________________________________________ You don't need to buy Internet access to use free Internet e-mail. Get completely free e-mail from Juno at http://www.juno.com/getjuno.html or call Juno at (800) 654-JUNO [654-5866]