To know the working or fetch operation of the 8085 microprocessor, we should know the timing diagram of 8085 microprocessor. With the help of the timing diagram, we can easily calculate the execution time of instruction as well as the program. Before going for a timing diagram of 8085 microprocessors we should know some basic parameters to draw a timing diagram of 8085 microprocessors. Those parameters are
Instruction Cycle
Machine cycle
T-state.
Instruction Cycle
Instruction cycle is the total time taken for completing one instruction execution
Machine cycle
The machine cycle is the time required to complete one operation such as accessing either the memory or an I/O device.
T-state
T-state is the time corresponding to one clock period. It is a basic unit used to calculate the time taken for the execution of instructions and programs in a processor.
What are the control signals used in the timing diagram of 8085 microprocessors?
Mainly we have to know five control signals to understand the timing diagram of 8085 microprocessors. Those are:
IO/ M'
IO/ M signal indicates whether I/O or memory operation is being carried out. A high on this signal indicates I/O operation while a low indicates memory operation.
S0 and S1
S0 and S1 indicate the type of machine cycle in progress.
ALE
ALE has indicated the availability of a valid address on the multiplexed address/data lines. When it is high act as an address bus and low act as a data bus.
RD'
Read is an active-low signal that indicates that data is to be read from the selected memory or I/O device through a data bus.
WR’
Write is an active-low signal that indicates that data on the data bus is to be written form the selected memory or I/O device.
