Hi all,

        I am having some problems with an icepic emulator. Specifically the
ADC. When the emulator probe is removed from the circuit, everything
operates normally. When the emulator is probe is inserted, one of the ADC
inputs jumps to 5.6V. The others work just fine. I checked RF Solution's
FAQ, but that wasn't of much use. I've been trying to pin this down without
much luck so far. Maybe someone has encountered something similar. Or i'm
overlooking something obvious. Anyway, here are the details:

        target is a 16F877. 5V, 4MHz.
        ADC clock runs at Fosc/8.
        AN3 is an external 5V reference (AD586)
        AN4, AN2, AN1, AN0 are analog inputs. PortE is digital input

        AN0 comes from an instrumentation amplifier (INA125), 221 Ohm
resistor in series
        AN1 is an external 2.5V reference (derived from the INA125)
        AN2 comes from another instrumentation amplifier (INA125), also a
221 Ohm resistor in series
        AN4 is floating (PCB layout oversight).

        So, as stated above, with no emulator installed, everything is just
peachy. When I install the emulator, AN2 becomes 5.6V. AN0 and AN1 behave
normally and convert correctly. The emulator shows the proper settings on
the TRISA bits, ADCON0, and ADCON1. FYI, this is a test fixture to be used
by a contract manufacturer on one of our circuit boards. Hence the two
identical amplifiers, one from the device under test, the other used as a
reference.

        Any thoughts?

Phil Eisermann
Electronics Engineer
The Ridge Tool Company
(440)329-4680

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