Serial Communication Questions and Answers

Q: The register which acts as 'receive' and 'transmit' buffer in serial communication in 8051 is :

The register is SBUF.SBUF (serial buffer) at SFR address 99H is really two registers at one address: writing to it loads the transmit buffer and starts transmission, and reading it returns the byte received.SCON is the serial control register, which sets the mode and holds the TI and RI flags. PCON holds the SMOD bit that doubles the baud rate, among power control bits. The accumulator only passes data to and from SBUF; it is not the serial buffer.

Q: Which of the following communication systems is not suitable in IoT integration ?

The key is I2C, and the other candidate is IRDA.Bluetooth and WiFi are wireless links that connect IoT devices to phones, gateways and the internet, so they are suitable. I2C is a two-wire serial bus for connecting chips on one board over a short distance, such as a sensor to a microcontroller. It is not a link between separate devices or to a network, so the key treats it as not suitable for IoT integration. It is, however, widely used inside IoT devices.IRDA is infrared, short range and needs a clear line of sight, which also limits it for IoT. The question gives no basis for ranking the two, so this follows the key.

Q: Which of the following signal controls the flow of data ?

The key's answer is RTS and DTR.In RS-232 serial communication, hardware handshaking signals control when data may be sent. RTS (Request To Send), answered by CTS, tells the other device that a terminal wants to transmit, and DTR (Data Terminal Ready), answered by DSR, tells it that the terminal is ready. Together these control signals manage the flow of data between the DTE and the DCE, so the combined option is the complete answer.Naming RTS or DTR alone gives only one of the two handshake lines. ECNR is not an RS-232 signal.

Direction for [ Question No: 1 To 1 ] :

Directions : The following items consist of two statements, one labelled the "Assertion (A)" and the other labelled the "Reason (R)". You are to examine these two statements carefully and decide if the Assertion (A) and the Reason (R) are individually true and if so, whether the Reason is a correct explanation of the Assertion. Select your answers to these items using the codes given below and mark your answer accordingly.

Assertion (A) : In serial communication system, when the transmission of data goes in both ways, it is called full-duplex system. Now if two micro processors are connected in full duplex mode, the amount of data transmitted will be double to the amount of data in half-duplex mode connection.
Reason (R) : When the transmission of data goes in one way, it is called half-duplex system and when the data moves in both ways, it is called full duplex system.

A.Both (A) and (R) are correct and (R) is correct explanation of (A).
B.Both (A) and (R) are correct, but (R) is not correct explanation of (A).
C.(A) is true, but (R) is false.
D.(A) is false, but (R) is true.

Exam Year(s)

UGC NET - 2014,

Answer: D

Following the official key, the Assertion is false and the Reason is true. The Reason correctly defines half duplex (data one way at a time) and full duplex (data both ways at once). The Assertion claims that the amount of data in full duplex will be double that of half duplex, which depends on the link and the traffic, so it is not true as a general statement.

The first half of the Assertion only repeats the definition, but its conclusion about doubling is the part judged wrong.

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The register which acts as 'receive' and 'transmit' buffer in serial communication in 8051 is :

A.SCON
B.PCON
C.SBUF
D.Accumulator

Exam Year(s)

MH SET - 2018, SET Exam - 2018,

Answer: C

The register is SBUF.

SBUF (serial buffer) at SFR address 99H is really two registers at one address: writing to it loads the transmit buffer and starts transmission, and reading it returns the byte received.

SCON is the serial control register, which sets the mode and holds the TI and RI flags. PCON holds the SMOD bit that doubles the baud rate, among power control bits. The accumulator only passes data to and from SBUF; it is not the serial buffer.

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Which of the following communication systems is not suitable in IoT integration ?

A.Bluetooth
B.WiFi
C.IRDA
D.I2C

Exam Year(s)

MH SET - 2023, SET Exam - 2023,

Answer: D

The key is I2C, and the other candidate is IRDA.

Bluetooth and WiFi are wireless links that connect IoT devices to phones, gateways and the internet, so they are suitable. I2C is a two-wire serial bus for connecting chips on one board over a short distance, such as a sensor to a microcontroller. It is not a link between separate devices or to a network, so the key treats it as not suitable for IoT integration. It is, however, widely used inside IoT devices.

IRDA is infrared, short range and needs a clear line of sight, which also limits it for IoT. The question gives no basis for ranking the two, so this follows the key.

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Which of the following signal controls the flow of data ?

A.RTS
B.DTR
C.RTS and DTR
D.ECNR

Exam Year(s)

MH SET - 2025, SET Exam - 2025,

Answer: C

The key's answer is RTS and DTR.

In RS-232 serial communication, hardware handshaking signals control when data may be sent. RTS (Request To Send), answered by CTS, tells the other device that a terminal wants to transmit, and DTR (Data Terminal Ready), answered by DSR, tells it that the terminal is ready. Together these control signals manage the flow of data between the DTE and the DCE, so the combined option is the complete answer.

Naming RTS or DTR alone gives only one of the two handshake lines. ECNR is not an RS-232 signal.

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Serial Communication Questions and Answers

Direction for [ Question No: 1 To 1 ] :

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Serial Communication Questions and Answers

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