Write a $20$ ms time delay subroutine using register pair BC$.$ Clear the $2$ flag with$-$ out affecting any other flags in the flag register and return to the main program.

$11.$ Write a program to control a railway crossing signal that has two alternately flash$-$

ing red lights, with a $1-$second delay on time for each light.

$12.$ Write a program to simulate a flashing yellow light with $750$ ms on time. Use bit Dy to control the light. $($Hint: To simulate flashing, the light must be turned off.$)$