Saturday, August 28, 2010


The MPu performs primarily four operations:
1. Memory Read : Read data from memory .
2. Memory Write : write data into memory.
3. I/o read : accept data from input devices.
4. I/O write: send data to output devices.

all these operations are part of the communication process between the MPU and peripherals devices . To communicate with a peripheral , the MPU needs to perform following steps.

step 1: identify the peripheral or the memory location.
step 2.: transfer binary information
step 3: provide timing or synchronization signals.

the 8085 MPU perform these functions using three sets of communication lines called buses:these address bus , and the control bus called system bus.

the address bus is a group of 16 lines generally identified as A0 to A15. The address bus is unidirectional :bits flow in one direction - from MPU to Peripherals devices. the MPU uses the address bus to perform the first function identifying a peripheral or a memory location.

in a computer system each peripherals or memory location is identified by binary number, called the address and the address bus is used to to carry a 16 bit address. this is similar to the postal of a house. a house can be identified by various number by two digit number scheme for example, the 45 th house in a lane can be identified by two digit number 45 or 0045 . the two digit numbering scheme can identified only a hundred house from 0000 to 9999 . similarly , the number of address lines of the MPU determine it's capacity to identify the different memory location . the MPU with its 16 address line is capable of addressing 2^16=65,536 known as 64 K memory location..
Most 8 bit processor have 16 bit address line . this may explain why micro-computer systems based on 8 bit micro-processors have 64 K memory . however ,not every micro-computer system have 64 K memory .In fact most single board micro-computers have less than 4 K memory , even if the MPU is capable of addressing 64 K memory . The number of address lines is arbitrary ; it is determined by the designer of a micro-processor based on such considerations as availability of pins and intended applications of the processors . For example the intel 8085 processors have 20 and the Pentium processor has 32 address lines.


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Haddock said...

That is informative.

Haddock said...

That is informative.


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