Which register use for serial communication?

Question

Examoogle · Accepted Answer

SBUF

Explanation: In the 8051 microcontroller, SBUF (Serial Buffer) is the primary register used for serial communication. It is a dual-purpose register: writing to it initiates transmission by loading the data into the Transmit Shift Register, and reading from it retrieves data received into the Receive Buffer.

Working Principle: When data is written to SBUF, it is transferred to the transmit shift register and shifted out serially via the TXD pin. When data is received via the RXD pin, it is shifted into the receive shift register and then moved to SBUF, where the CPU can access it. SBUF acts as an interface between the internal data bus and the serial communication hardware.

Key Formulas: $Baud Rate = \frac{Timer 1 Overflow Frequency}{32} 	imes k$; $SBUF = Data_{transmit} / Data_{receive}$

Key Points: SBUF is physically two separate registers mapped to the same address (99H).; Writing to 99H accesses the Transmit Buffer.; Reading from 99H accesses the Receive Buffer.; Serial communication modes are controlled by the SCON register.

Advantages: Simplifies data transfer between microcontroller and peripheral devices.; Supports full-duplex communication.

Disadvantages: SBUF is not bit-addressable.; Requires proper baud rate configuration in Timer 1 for accurate data transfer.

Applications: UART serial communication; Interfacing with PC/Serial terminals; Multi-processor communication

Additional Info: SCON (Serial Control) register controls the mode of operation and interrupt flags.. PCON (Power Control) register contains the SMOD bit which affects baud rate.. IP (Interrupt Priority) register is used to manage interrupt priorities, not serial data itself.

Answer: A is correct — SBUF is the specific register used in the 8051 for holding data to be transmitted or data that has been received via the serial port.

Exam Tip: Remember that while SCON handles the mode configuration and status flags, SBUF is exclusively for the raw data payload transport.

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