input output instructions 8051 assembly language

Posted on Feb 5, 2014

This tutorial is in continuation with previous tutorials on 8051 Assembly Programming. Now we will learn how to give input and output instructions to 8051 microcontroller(s) using assembly programming language. The microcontroller has total forty pins in all. Most of the pins of 8051 microcontroller have more than one function. The first function

input output instructions 8051 assembly language
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is the input /output operation and the second function can be some special function like they can be used as counters or for serial communication. In microcontroller there are four ports (collection of pins) P0, P1, P2 &P3. These ports have 8 pins each as shown. As we will see later on we will be able to address the whole port during programming. Whenever we are talking about 8051 we are talking of the family of microcontrollers having the architecture of 8051. They are all same except for some additional features, pins distribution and packaging. VCC and GND: - The pin 40 is Vcc i. e. it is given 5V and pin 20 is GND i. e. it is given 0V (supplied from power source) for powering up the microcontroller. CONNECTING THE CRYSTAL (XTAL1- XTAL2): The pin numbers 18 - 19 are used to connect the crystal. The frequency of this crystal determines the machine cycle. With 8051 family we can use a crystal having frequency from 3 to 24 MHz. RESET PIN CONNECTION (RST): The reset pin i. e. pin number 9 is used to reset the program just like we restart a computer, the program starts executing from the very beginning. When reset is used the program counter is set back to zero and the values in all other registers are lost. EA/VPP: The EA pin no. 31 is known as external access. The 8051 microcontrollers have on chip ROM so the EA/VPP is set to one (or Vcc). In case there is no on- chip ROM, like in case of 8031 we set this pin equal to zero....

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