MICROPROCESSOR COMMUNICATION AND BUS TIMING

MICROPROCESSOR COMMUNICATION AND BUS TIMING

To understand the function of various signals of the 8085 , we should examine the process of communication ( reading from the and writing into the memory ( for example when a boy read his lesson, data write to his brain . when he told to someone data is read from his brain in the same manner this process happen in micro-processor)) between the micro-processor and memory and the timing of these signal in relation to the system clock . The first step in the communication process is reading from memory or (fetching the instruction )

• a courier gets the address from the office ; he or she drives pickup van ,find your home address ( you have one home name or address) so he can find your home if he know the address or name . we know that MAR hold address.
• The courier ring bell. So you can know that some one there in front of your home. same way register can know when it is selected
• Somebody in the house open the door and give packages to the courier, and the courier return to the office with the packages. In our discussion data is for read or write. data is gone through bus ( AD0-AD7) to its destination
• Internal office staff check the packages according to the instruction given by the customer

Now let study how the micro processor works. Fetching or get a machine code from memory

Resent logic levels of group of lines; some lines are high and other are low . the crossover of the lines indicates that new bytes( information) is placed on the , and a dashed straight line indicates the high impedance state . to fetch the byte , MPU perform the following steps

when we draw the timing diagram there are two onefor op code fetch and other for memory read or write.op code fetch containing for 4 cycle,memory read or write containing 3 cycle.it's general , if we have more instruction cycle increase accordingly.

Labels: Micro-Processors