Question

Build the 7-segment decoder for BCD using a ROM (in logisim)

Answer 1

First open the logisim tool.Then select the ROM and drag it into the workspace.Change the address length to 4 and data bits width to 7.This is because for a 7 segment display we have only a,b,c,d,e,f,g outputs and the input ranges from 0 to 9 which requires 4 bits to represent 0 to 9.

Now right click on the rom and change the rom contents.Enter the hexa value of a to g. Just see the circuit diagram below you will get it.

Now take a pin from the wiring section and connect it to the Address line A of the ROM.Just adjust the pin width to 4 by clicking.

Now connect another pin to the output of the ROM that is data bits adjust the pin width is 7 here.

Now take a seven segment display into the work space.

Take a splitter with input width 7 and output width is 7.Connect this to D of the ROM.

Now connect the output data bits from the splitter to the seven segment display like shown below of the pin configuration.

Here the dot pin should be high to on the display.

Now go to the base section and select the poke tool to changes the values in input pin.Just take the hand on the x value which changes the values from 0,1,x. Select your combination and see the 7_Segment decoder values on the output pin.

The circuit diagram and simulation results:

In the rom just observe that for the input address that data is highlighted with the black color.

So there are the hex values of the decoder i stored in the rom.

These are output for the some of the inputs.You can verify the remaining inputs also.

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