This set of 8051 Micro-controller Multiple Choice Questions & Answers (MCQs) focuses on “Interfacing with 8255”.
1. What is the function of 8255 chip?
a) the ports of 8255 can act as the input/ output port for the micro controller
b) it is a type of an external memory device that is being interfaced with the micro controller
c) both of the mentioned
d) none of the mentioned
Explanation: 8255 is an IC that is used to increase the number of input/output ports of a micro controller. As its ports offer an advantage of increasing the number of ports for interfacing external devices.
2. Which pins of a micro controller are directly connected with 8255?
d) all of the mentioned
Explanation: RD, WR, D0-D7 all are directly connected to the 8051 for telling the chip about the control signals and also for transferring the data.
3. Find the control word for PA= out, PB= in, PCL=out, PCH=out (Mode0)?
Explanation: The value that is being loaded in the control word is 10000010b for PB as an input port ans all others as the output ports being operated in mode0.
4. Which pins are used to select the ports and the control register?
d) All of the mentioned
Explanation: CS, A0, A1 all are used to select the ports and the control register of 8255.
5. What is the value of the control register when RESET button is set to zero?
d) value remains the same as was before the RESET button was set to zero
Explanation: RESET button makes the value of the control register clear if an active high pulse is applied to it. So for clearing the control register RESET button should be set to 1.
6. Why MOVX instruction is being used to access the ports of the 8255?
a) because 8255 is used to access the memory mapped I/O
b) because 8255 is used to access the external communication
c) because 8255 is used to access the data transfer
d) because 8255 is used to access the interfacing of LCD, motor etc.
Explanation: MOVX instruction is used to access the external memory, so it is used to access the memory mapped I/O.
7. What is correct about the BSR mode from below?
a) it is active low input used to select the individual bits of the PORTA
b) it is active low input used to select the individual bits of the PORTB
c) it is active low input used to select the individual bits of the PORTC
d) none of the mentioned
Explanation: BSR is used to select the individual bits of the PORTC. It is the D7 bit of the control register.
8. How many pins of the 8255 can be used as the I/O ports?
Explanation: There are 3 ports available in the 8255 so 24 pins are available for the I/O ports pins.
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