Test Products International 440 - Manual (Page 27)

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k. Logic Test
The logic state of IC’s can easily be determined with the 440.
Use the function buttons to select TTL, 3V CMOS or 5V CMOS
logic chips. The 440 will display high and low logic levels.
TTL 3V 5V
CMOS CMOS
F1 F2 F3 F4 F5
This function is designed to check the HI/LOW logic states of
IC’s and circuits by direction of the arrow on the LCD. For TTL
circuits, the arrow will point downward at or below 2.9 volts
and upward at or above 3.2 volts. For 3V CMOS the arrow will
point downward at or below 1.7 volts and upward at or above
2.0 volts. For 5V CMOS the arrow will point downward at or
below 3.1 volts and upwards at or above 3.4 volts. When the
BZ is also activated, the 440 buzzer will sound when HI logic
levels are measured.