Question

Which of the following steps detects the key in a 4*4 keyboard matrix about the key that is being pressed?

(a) masking of bits

(b) ensuring that initially, all keys are open

(c) checking that whether the key is actually pressed or not

(d) all of the mentioned

I have been asked this question in a national level competition.

The origin of the question is Keyboard Interfacing in division 8051 Microcontroller of Microcontroller

Answer 1

Right answer is (d) all of the mentioned

Easy explanation: For detecting that whether the key is actually pressed or not, firstly this must be ensured that initially all the keys are closed. Then we need to mask the bits individually to detect that which key is pressed. Then we need to check that is the key actually pressed or not, by checking that whether the key pressed for a time more than 20 micro seconds.