Microprocessor has following instructions to perform:


  1. Reading instructions or data from program memory ROM.
  2. Interpreting the instruction and executing it.
  3. Microprocessor Program is a collection of instructions stored in a  
  4. Nonvolatile memory.
  5. Read Data from I/O device
  6. Process the input read, as per the instructions read in program memory.
  7. Read or write data to Data memory.
  8. Write data to I/O device and output the result of processing to O/P device.



           Microprocessors brought the concept of programmable devices and made many applications of intelligent equipment. Most applications, which do not need large amount of data and program memory, tended to be costly.

                 The microprocessor system had to satisfy the data and program requirements so; sufficient RAM and ROM are used to satisfy most applications .The peripheral control equipment also had to be satisfied. Therefore, almost all-peripheral chips were used in the design. Because of these additional peripherals cost will be comparatively high.

An example:

8085 chip needs:         

           An Address latch for separating address from multiplex address and data.32-KB RAM and 32-KB ROM to be able to satisfy most applications. As also Timer / Counter, Parallel programmable port, Serial port, and Interrupt controller are needed for its efficient applications.  

          In comparison a typical Micro controller 8051 chip has all that the 8051 board has except a reduced memory as follows.

4K bytes of ROM as compared to 32-KB, 128 Bytes of RAM as compared to 32-KB.          


On comparing a board full of chips (Microprocessors) with one chip with all components in it (Micro controller).


          Lots of Microprocessor circuitry and program to debug. In Micro controller there is no Microprocessor circuitry to debug.

Slower Development time:

As we have observed Microprocessors need a lot of debugging at board level and at program level, where as, Micro controller do not have the excessive circuitry and the built-in peripheral chips are easier to program for operation.

                                                So peripheral devices like Timer/Counter, Parallel programmable port, Serial Communication Port, Interrupt controller and so on, which were most often used were integrated with the Microprocessor to present the Micro controller .RAM and ROM also were integrated in the same chip. The ROM size was anything from 256 bytes to 32Kb or more. RAM was optimized to minimum of 64 bytes to 256 bytes or more.



7.1.1 PIC 16F877A microcontroller:


It is used here to display message on the Hitachi HD44780-based character LCD module. PIC16F877A is 8-bit microcontroller based on reduced instruction set computer


(RISC) architecture. It has 8kx14-bits flash program memory, 368 bytes of RAM.


                    Here PIC16F877A microcontroller is connected to HD44780 LCD in 4-bit interface data, only four bus lines (DB4 to DB7) are used for data transfer. Bus lines DB0 to DB3 are having no connection with microcontroller. The data transfer between the HD44780U and the PIC16F877A is completed after the 4-bit data has been transferred twice. 

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Wed, 22/06/2011 - 12:06