Can somebody help with with designing a RISC and MIPS based 4bit CPU?

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So a friend and I have a project to design a CPU and we are stuck. I would really appreciate some help and instructions on how to do this.

Design a CPU using the MIPS and RISC instruction set for the following OpCodes and implement into Logisim.

The main components are the RAM, ROM, PLA programming to work with these.

Linked are the Logisim program and the diku library to go with it. The diku has the PLA, ROM, RAM ready to be programmed but I am unsure how.

I don't know any electrical engineering forums that would be actually able to help. I would be happy if someone could link to a better place to post this.

Logisim
http://sourceforge.net/projects/circuit/files/2.7.x/2.7.1/logisim-generic-2.7.1.jar/download

PLA
https://github.com/downloads/andersbll/logisim-diku/logisim-diku-1.1.jar


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Here is my Harvard architecture CPU. nice and easy to program. Little bit messy but it works so whatever.