Question

When a key is pressed, a debounce logic comes into operation in

(a) scanned keyboard special error mode

(b) scanned keyboard with N-key rollover

(c) scanned keyboard mode with 2 key lockout

(d) sensor matrix mode

I got this question by my school principal while I was bunking the class.

I would like to ask this question from the Keyboard/Display Controller 8279 in division Special Purpose Programmable Peripheral devices and their Interfacing of Microprocessor

Answer 1

Right answer is (c) scanned keyboard mode with 2 key lockout

The best explanation: In scanned keyboard mode with 2 key lockout mode of operation, when a key is pressed, a debounce logic comes into operation. During the next two scans, other keys are checked for closure and if no other key is pressed then the first pressed key is identified.