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


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? 


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. 


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. 


1. "RR A" is changed to "RL A". 

2. True

3. True 

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