TABLE OF CONTENTS Before one uses the microcontroller, he or she should be well aware of the connections of the microcontroller, like which pins are to be used as data pins and which pin is to be given the power supply. Every pin of the microcontroller has a specific function and a wrong connection can completely destroy the chip. The AT89C51 microcontrollers have, in total, 40 pins. Here we will be demonstrating the pin configuration of the 8051 microcontroller. It has an onchip RAM capacity of 128 bytes and ROM size is 4k. But the total ROM size with which it can work is 64k. So when we have programs of size more than 4k, external memory is added to it as per our requirement. If the requirement is of 8k, we can go for an external ROM of size 4k such that it makes a total ROM size of 8k (4k internal + 4k external). In this way we can go for 8k, 16k, 32k, and 64k ROM sizes.
We have different commands for using these memories. Accordingly some of the connections are to be changed. For example, if our program size is below 4k then the 31 st pin, which is for external access, is to be given a power supply of 5 volts (an active low pin) but while using external memory we have to ground this pin. We can also use both internal as well as external memories simultaneously, in...
