Engineering Questions with Answers - Multiple Choice Questions

# MCQs on Interfacing With 8051 Ports -1

1 - Question

Which of the following is not one of the SFR addresses of the ports of 8051?
a) 80H
b) 90H
c) A0H
d) NONE

Explanation: The SFR addresses of the ports P0, P1, P2 and P3 are 80H, 90H, A0H and B0H respectively.

2 - Question

Each port line of a port can individually source a current of upto
a) 0.2 mA
b) 0.25 mA
c) 0.5 mA
d) 0.75 mA

Explanation: Each port line of a port can individually source a current of upto 0.5 mA.

3 - Question

Each port line of a port can individually sink a current of upto
a) 2 mA
b) 8 mA
c) 5 mA
d) 1 mA

Explanation: Each port line of a port can individually sink a current of upto 8 mA.

4 - Question

The number of TTL inputs that can be sinked by the port 0 when a logic 0 is sent to a port line as an output port is
a) 2
b) 4
c) 6
d) 8

Explanation: When a logic 0 is sent to a port line as an output port, it can sink 8 LS TTL inputs. Port 0 is used as data bus during external interfacing whenever required.

5 - Question

The open drain bidirectional (input or output) port with internal pullups is
a) Port 0
b) Port 1
c) Port 2
d) Port 3

Explanation: Port 0 is an open drain bidirectional (input or output) port with internal pullups. Port 1, Port 2, Port 3 are 8-bit bidirectional ports.

6 - Question

The port that can source or sink 4 LS TTL inputs when being used as an output port on each of its line is
a) Port 1
b) Port 2
c) Port 3
d) all of the mentioned

Explanation: The ports P1, P2 and P3 can source or sink 4 LS TTL inputs when being used as an output port on each of its line.

7 - Question

The port that will source a current of 500 micro amperes when being used as input ports is
a) 0.5 mA
b) 0.25 mA
c) 250 micro amperes
d) 500 micro amperes

Explanation: Port 3 pins which are externally pulled low when being used as input pins will source current of 500 micro amperes.

8 - Question

If the EA(active low) signal is grounded then the execution
a) directly start from main memory
b) directly start from 16 bit address in main memory
c) directly start from 16 bit address in program memory
d) directly start from RAM

Explanation: For interfacing external program memory, EA(active low) pin must be grounded. If the EA(active low) signal is grounded then the execution will start directly from the 16-bit address 0000H in external program memory.

9 - Question

When the port lines of a port are to be used as input lines then the value that must be written to the port address is
a) F0H
b) 0FH
c) FFH
d) 00H

Explanation: When the port lines of a port are to be used as input lines then ‘FF’H must be written to the port address.

10 - Question

Port 1 lines are used during programming of
a) external EPROM and EEPROM
b) external ROM and RAM
c) internal ROM and RAM
d) internal EPROM and EEPROM

Explanation: Port 1 lines are used as lower byte of 16-bit address bus during programming of internal EPROM or EEPROM.

11 - Question

The configuration in which each LED receives operating current of 8 mA from power supply while the port lines sink the current on each port line is
a) common port configuration
b) common anode configuration
c) common cathode configuration
d) none of the mentioned