The LED display is the one that display the value of the Key pressed and also the result of the computation.
The figure above show the LED display and all the circuit that make it display numeric information. The component containing 3 in four places is the shift Register. It has four aspect of it. On the left side we have three pins, one to enable serial shift or disable it, the second is for the input of numeric data, the third is the clock. The clock is for updating the information entering the register.
On the left side is the serial output. Above and below are the parallel input and parallel output. simultaneous information are loaded through the parallel input and can be output serially or in parallel.
For our Calculator, we have Ten input OR gate to output each key pressed. These input are the tunnels of each keys. A tunnel showing DATA is the result of the key pressed at any point in time. The Register has four stages to represent four digits on the Display (when you choose your register, change the property to four stages and four bits). The moment the digits are exhausted the second OR gate come into action igniting the negated part of the AND gate joining it with first OR gate to stop further input into the Shift Register. Under the register is the first pin which can be used to clear the screen. An input with zero is attached to it. And when it is one the screen will clear.
To create your LED display, choose Hex Digit Display from the Input/Output folder and put four of it beside each other as shown on the diagram. To make the LED Display to show the key pressed from the right, connect the LED on the right to the first stage of the shift register as shown, the second LED to the right to the second stage of the Register and so on. Also notice that the Second OR gate to stop the display when it is full is connected to the last stage of the Shift register. So that the moment the fourth stage is occupied it trigger the AND gate to stop further input.
PLEASE CHECK BACK FOR THE 3RD PART WHICH HAS TO DO WITH PROCESSING AND CALCULATIONS.
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