Test: Keyboard Interfacing - Computer Science Engineering (CSE) MCQ

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 that 20 micro seconds.

This particular command CJNE A,#00001111b, ROW1 compares the value of the accumulator with OFH and jumps to ROW1 address if the value is not equal.

We can mask or we can even rotate the bits to check that particularly in which column is the key placed.

If no key is pressed, then all the keys show 1 as they are all connected to power supply.

If a key is to operate in an interrupt mode, than it will generate an external hardware interrupt.