Microprocessors Questions and Answers – Interfacing With 8051 Ports -2

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This set of Microprocessors Questions and Answers for Campus interviews focuses on “Interfacing With 8051 Ports -2”.

1. If EA(active low) signal =1, then the execution starts from
a) internal EPROM
b) flash RAM
c) internal EPROM or flash RAM
d) none
View Answer

Answer: c
Explanation: If EA(active low) signal =1, then the execution starts from an internal EPROM or flash RAM address 000H, can continue upto FFFH address and then for higher addresses it will go into external memory.
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2. The pin that is grounded for interfacing external EPROM is
a) EA(active low)
b) PSEN(active low)
c) OE(active low)
d) All of the mentioned
View Answer

Answer: a
Explanation: The EA(active low) pin is grounded for interfacing external EPROM. The PSEN(active low) is used for interfacing EPROM i.e. it acts as an OE(active low) input to EPROM.

3. The step that is involved in the procedure of memory interfacing with 8051 is
a) data bus is connected to data lines of memory chips
b) PSEN(active low) is connected to OE(active low) of EPROM chips
c) writing address map of memory chip in bit form
d) all of the mentioned
View Answer

Answer: d
Explanation: The procedure of memory interfacing with 8051 includes, data bus connection to data lines of memory chips, PSEN(active low) connected to OE(active low) of EPROM chips and writing address map of memory chip in bit form.

4. The device that is used for deriving chip select signals is
a) Logic gates
b) Multiplexers
c) PLAs and EPROMs
d) All of the mentioned
View Answer

Answer: d
Explanation: The logic gates and multiplexers are most commonly used for deriving chip select signals. The advanced circuits like PLAs and EPROMs are also used for deriving chip select signals.

5. For deriving chip selects of isolated memory or IO devices, the gates that are traditionally used are
a) NOR and NAND
b) NAND and NOT
c) NOT and NOR
d) AND, OR and NOT
View Answer

Answer: b
Explanation: For deriving chip selects of isolated memory or IO devices, the NAND and NOT gates are traditionally used.
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6. The current that is required for a LED for an appropriate glow is
a) 6-8 mA
b) 4-6 mA
c) 8-10 mA
d) 10-12 mA
View Answer

Answer: c
Explanation: For appropriate glow, a LED typically requires 8-10 mA with around 1.6 Volts.

7. The maximum current that can be sinked totally by all the ports of 8051 is
a) 61 mA
b) 81 mA
c) 91 mA
d) 71 mA
View Answer

Answer: d
Explanation: All the ports together (4 ports) should not be made to sink more than 71 mA.

8. The number of LEDs that can be connected to a port of 8051, if all are expected to glow simultaneously is
a) 6
b) 8
c) 10
d) 12
View Answer

Answer: b
Explanation: If 8 LEDs are connected to a port of 8051, and if all are expected to glow simultaneously, the total current sinked by the 8051 port will be 8×8=64 mA (since min voltage for an LED to glow=8 mA) which is less than the maximum 71 mA.

9. Which is true in interfacing 7 segment code display?
a) transmitted by second port
b) display is selected by third port
c) display is selected by second port
d) none of the mentioned
View Answer

Answer: c
Explanation: The 7-segment code of a digit is transmitted by the first port and the display is selected by second port. As soon as the display is selected by the second port, the digit starts glowing on that display position.
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10. After the display is selected by second port, then the digit (LED) glows for a duration of
a) 5 msec
b) 10 msec
c) 2 msec
d) 6 msec
View Answer

Answer: a
Explanation: The unit(LED) glows for a duration of 5 msec.

11. The number of scans of the complete 8-digit display that can be carried out in one second is
a) 15
b) 25
c) 35
d) 55
View Answer

Answer: b
Explanation: Starting from either right most or left most digit, every digit glows for 5 msec one by one. Thus one scan of the 8 digit display requires 40 msec. Thus in one second, 25 scans of the complete 8-digit display can be carried out.

12. To convert its current output into a voltage, the DAC 0808 is connected with
a) Transistor(BJT) externally
b) FET externally
c) OPAMP externally
d) OPAMP internally
View Answer

Answer: c
Explanation: the DAC 0808 is connected with OPAMP externally, to convert its current output into voltage.

Sanfoundry Global Education & Learning Series – Microprocessors.

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Here’s the list of Best Reference Books in Microprocessors.

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He is Linux Kernel Developer & SAN Architect and is passionate about competency developments in these areas. He lives in Bangalore and delivers focused training sessions to IT professionals in Linux Kernel, Linux Debugging, Linux Device Drivers, Linux Networking, Linux Storage, Advanced C Programming, SAN Storage Technologies, SCSI Internals & Storage Protocols such as iSCSI & Fiber Channel. Stay connected with him @ LinkedIn