Microprocessors Questions and Answers – Programmable Communication Interface 8251 USART

This set of Microprocessor Multiple Choice Questions & Answers (MCQs) focuses on “Programmable Communication Interface 8251 USART”.

1. Which of the following is not a mode of data transmission?
a) simplex
b) duplex
c) semi duplex
d) half duplex
View Answer

Answer: c
Explanation: Basically, there are three modes of data transmission. simplex, duplex and half duplex.

2. If the data is transmitted only in one direction over a single communication channel, then it is of
a) simplex mode
b) duplex mode
c) semi duplex mode
d) half duplex mode
View Answer

Answer: a
Explanation: In simplex mode, the data transmission is unidirectional. For example, a CPU may transmit data for a CRT display unit in this mode.

3. If the data transmission takes place in either direction, but at a time data may be transmitted only in one direction then, it is of
a) simplex mode
b) duplex mode
c) semi duplex mode
d) half duplex mode
View Answer

Answer: d
Explanation: In half duplex mode, data transmission is bidirectional but not at a time. For example, Walkie-Talkie.
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4. In 8251A, the pin that controls the rate at which the character is to be transmitted is
a) TXC(active low)
b) TXC(active high)
c) TXD(active low)
d) RXC(active low)
View Answer

Answer: a
Explanation: Transmitter Clock Input (TXC(active low)) is a pin that controls the rate at which the character is to be transmitted.

5. TXD(Transmitted Data Output) pin carries serial stream of the transmitted data bits along with
a) start bit
b) stop bit
c) parity bit
d) all of the mentioned
View Answer

Answer: d
Explanation: Transmitted Data Output pin carries a serial stream of the transmitted data bits along with other information like start bits, stop bits and parity bits etc.
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6. The signal that may be used either to interrupt the CPU or polled by the CPU is
a) TXRDY(Transmitter ready)
b) RXRDY(Receiver ready output)
c) DSR(active low)
d) DTR(active low)
View Answer

Answer: b
Explanation: RXRDY(Receiver ready output) may be used either to interrupt the CPU or polled by the CPU.

7. The disadvantage of RS-232C is
a) limited speed of communication
b) high-voltage level signaling
c) big-size communication adapters
d) all of the mentioned
View Answer

Answer: d
Explanation: RS232C has been used for long and has a few disadvantages like limited speed of communication, high-voltage level signaling and big-size communication adapters.
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8. The USB supports the signaling rate of
a) full-speed USB 1.0 at rate of 12 Mbps
b) high-speed USB 2.0 at rate of 480 Mbps
c) super-speed USB 3.0 at rate of 596 Mbps
d) all of the mentioned
View Answer

Answer: d
Explanation: The USB standards support the signaling rates. Also, USB signaling is implemented in a differential in low- and full-speed options.

9. The bit packet that commands the device either to receive data or transmit data in transmission of USB asynchronous communication is
a) Handshake packet
b) Token packet
c) PRE packet
d) Data packet
View Answer

Answer: b
Explanation: The token packet is the second type of packet which commands the device either to receive data or transmit data.
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10. High speed USB devices neglect
a) Handshake packet
b) Token packet
c) PRE packet
d) Data packet
View Answer

Answer: c
Explanation: PRE packets are only of importance to low-speed USB devices.

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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