Many situations may arise, where a microcomputer system requires accurate time delays. For example, when we implement a real time clock, the time needs to get updated at least for once in every second.
We generate accurate time delays by using a few instructions in a loop.It is completely software based, where 8085 does not perform any work which is beneficial except the generation of time delays.
The delay in time or Time delay scan also be generated by hardware method also. As an example, a 555 timer chip can also be used for the generation of time delays or delay in time. Here the time delay is generated which is totally depending on the resistor and capacitor component values. These R and C components have a tolerating capacity of 10%. Hence the delay in time is not accurate, but the processor can do the other processing task.
Now in order to get the exact the exact delay in time rather time delays by the hardware, timer chips which are programmable like Intel 8253 are used. Here, very little software overhead is required and the processor is available for other processing.
As a DIP package Intel 8253 is a 24-pin programmable IC available. IC has three counters which work independently and whose width is of 16-bits. In addition, we have a control port to decide what is the mode of working of the three counters. The physical and functional pin diagrams of them are indicated below.
Fig.Diagram of 8253 pin based
Fig.Pin diagram functional