04. a) Write an 8051 C program to send values 00 through FFH to port Pl. b) Write an 8051 C program to send values -3 to +3 to port P1. c) Write an 8051 C program to toggle all bits of P1 (between 55H and AAH) with some delay. d) A door sensor is connected to P1.1 and a buzzer to P1.7. Write an 8051 C program to monitor the sensor and when it opens (0') sound the buzzer by sending a square wave of 50% duty cycle using the delay routine of 01