A keyboard is a very common input device. We assume that there are only eight keys for the simple keyboard. Whenever a key is pressed on this keyboard by the user, the microprocessor immediately identifies which key is pressed. The action which is to be performed by the processor depends on that particular key that gets pressed. An example to be cited as on a particular keyboard for calculator the addition operation gets performed when we press the ‘+’ key. Moreover, a microprocessor does not get directly communicated by the input device it is done via the input port. The input port is of tri-stated gates and a tri-stated buffer is of 7244 chip. There are total eight buffers which we arrange into two groups of four buffers with the outputs that are non inverted and are in tri-states. There is a short circuit between the input and the output when the enable pin is at logic 0. As well as there is an open circuit when the enable pin is at logic 1. We call the outputs to be the state of high impedance significantly called as tristate. Hence the 74244 the content of tristate buffer gets received in the 8085 accumulator when IN 77H gets executed.
In a microcomputer system there are many input devices which comprises the entire system.