Question

When a key is pressed, the debounce circuit waits for 2 keyboard scans and then checks whether the key is still depressed 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

This question was addressed to me in a dream while sleeping

Question is taken from the Keyboard/Display Controller 8279 in section Special Purpose Programmable Peripheral devices and their Interfacing of Microprocessor

Answer 1

Correct choice is (b) scanned keyboard with N-key rollover

Easy explanation: In this mode, When a key is pressed, the debounce circuit waits for 2 keyboard scans and then checks whether the key is still depressed. If it is still depressed, the code is entered in FIFO RAM.