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Analogue input for ADC higher than Vref

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swapan

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Hi,
External Vref of 16F72 MCU is clamped at 2.5V. What will happen to ADRES register returning equivalent digitized value of analogue input of 4.0V? Would it return 0xFF or otherwise? In practical hardware of a volt meter circuit I have noticed that when input is increased gradually from 0, correct values are shown upto 255. If the input is further increased, erratic lower values are shown.
 

See datasheet specification
A25 VAIN Analog Input Voltage VSS - 0.3 — VREF + 0.3

Doesn't seem to guarantee monotonicity above Vref.
 

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