During an 8051 microcontroller experiment, switches are connected to Port 1. Before reading the switch status, the program writes logic ‘1’ to the port pins. What is the purpose of this operation?
To configure the port pins as input
The 8051 ports are quasi-bidirectional: each pin has an internal weak pull-up but no separate direction register.
To use a pin as an input, the program must first write logic ‘1’ to it; this turns off the pin’s output driver transistor and leaves the pin held high through the weak pull-up so an external device can pull it low or leave it high.
If a ‘0’ were written instead, the pin would be driven hard low and an external switch could never raise it, so the switch state could not be read.
Writing ‘1’ therefore prepares (configures) the Port 1 pins to sense the external switches as inputs — it does not clear data, set output mode, or enable serial communication.
Hence, the answer is to configure the port pins as input.
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Important Questions from Microprocessors and Microcontrollers
Data and address bus width of 8085 microprocessor respectively are
How many bits are used in the data bus of 8051 ?
- Which of the 8051 ports need pull-up resistors to function as an I/O port?
How many bytes are used by the given data directive of the 8051 microcontroller?
DATA_1 DB "INDIA"
A. Microcontrollers are normally less expensive than microprocessors.
B. The 8051 microcontroller has three on-chip timers.
C. Mode 2 of 8051 timer is used to set the baud rate.
D. For the LCD to recognize information at the data pins as data, the register select (RS) pin must be set to low.
E. A driver must be placed between the micrcontroller and the stepper motor.
Choose the correct answer from the options given below:
