This set of Microprocessor Multiple Choice Questions & Answers (MCQs) focuses on “Interfacing With 8051 Ports -1”.
1. Which of the following is not one of the SFR addresses of the ports of 8051?
a) 80H
b) 90H
c) A0H
d) NONE
View Answer
Explanation: The SFR addresses of the ports P0, P1, P2 and P3 are 80H, 90H, A0H and B0H respectively.
2. 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
View Answer
Explanation: Each port line of a port can individually source a current of upto 0.5 mA.
3. 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
View Answer
Explanation: Each port line of a port can individually sink a current of upto 8 mA.
4. 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
View Answer
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. The open drain bidirectional (input or output) port with internal pullups is
a) Port 0
b) Port 1
c) Port 2
d) Port 3
View Answer
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. 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
View Answer
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. 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
View Answer
Explanation: Port 3 pins which are externally pulled low when being used as input pins will source current of 500 micro amperes.
8. 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
View Answer
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. 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
View Answer
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. 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
View Answer
Explanation: Port 1 lines are used as lower byte of 16-bit address bus during programming of internal EPROM or EEPROM.
11. 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
View Answer
Explanation: The common anode configuration is preferred to that of other configurations as in common anode configuration, each LED receives operating current of 8 mA from power supply while the port lines sink the current on each port line.
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