Logical operations in CMOS digital integration are highly prone to fail as the amount of power supply (PS) drop approaches to failure threshold. PS voltage variation is characterized by built-in noise monitors in a 32-bit microprocessor of 90-nm CMOS technology, and related with operation failures by instruction-level programming for logical failure analysis. Combination of voltage drop size and activated logic path determines failure sensitivity and class of failures. Experimental observation as well as simplified simulation is applied for the detailed understanding of the impact of PS noise on logical operations of digital integrated circuits.