Relay, Optoisolator, and Stepper Motor - Unit 15 - Review Questions & Answers from 8051 Microcontrollers & Embedded Systems by Mazidi

 SECTION 15.1: PROGRAMMING THE 8255 

1. Find the control byte if all ports are inputs.

2. Find the control byte for PC = in, PB = out, and PA = out. 

3. True or false. To avoid aliases, we must decode addresses A0 - A15.

4. Can 86H be the base address for port A of the 8255?

5. Why do we use the MOVX instruction to access the ports of the 8255? 

Answers: 

1. 9BH

2. 89H 

3. True

4. It cannot since we must have Al = 0 and AO = 0 for the base address. 

5. The MOVX instruction allows access to external memory and 8255 is mapped as memory-mapped I/0. 

SECTION 15.2: 8255 INTERFACING 

1. Modify the stepper motor program to turn counterclockwise.

2. True or false. In programming the LCD via an 8255 (without checking the busy flag), port A is always an output port.

3. True or false. In the LCD connection to the 8255, we must have a long delay before issuing the next data if we are not checking the busy flag. 

Answers: 

1. "RR A" is changed to "RL A". 

2. True

3. True