Basic Operations of 8085 Microprocessor

The 8085 microprocessor  performs followings  five  basic  operations .

1. Opcode Fetch :  Reading and decoding  operation code  of n instruction.

2. Memory Read: Reading data  from  memory.

3. Memory Write : Writing data  into  memory.

4. I. O Read: Accepting  data from  input  port.

5. I/ O  Write : Sending data  to output  port.

These  operations  will be  discussed in detail  with their  timing diagrams in  chapter6.

Here  only memory  read  operation is explained   to show  how  different  busses  are used  together  to perform  such  operations.

Suppose  data byte  stored  at location 2010H   is to be  read in  memory  read  operation  followings  steps are followed  to perform  this operations:

1. The 16 bit  memory  address is placed  on the 16bit  address bus by the microprocessor.

2. The address is decoded by  the memory  decoder  and the  desired  memory  location is selected.

3. For  reading  the data  from this  location  a RD signal  is generated by  the control  unit  of the  microprocessor  which  enables  the memory  chip.

4. The data  byte  from the  memory  location  is placed  on the  data bus.

5. Through  data bus data  byte is brought  into the  microprocessor  register.