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Reptile-4: The Hardware Design

Reptile FSM


Reptile Hardware

Reptile memory connection

Reptile FSM with Control Signals

Reptile Control Unit

We must have as many lines as the number of “balls” plus one line for JZ.

Each line contains as many bits as control signals plus one bit for Fetch.

The complete circuit for the control unit of Reptile is shown below. As can be seen, it is almost identical with the control unit of Frog. The only difference is the part drawn in red in the diagram below, which handles the conditional jumps, ie, the JZ instructions.


Reptile in Verilog




  1. Add an overflow flag into hardware. How you should change the instruction set to take advantage of this new flag?
  2. Add address offset to load and store instructions.
  3. Create conditional jump instructions for many different conditions, ie, not only JZ but JNZ, JEQ, JGT etc.
  4. Increase memory size to 64K while keeping the data size 16 bits. Which instructions will change?
  5. Add a monitor which shows the address and PC at each instruction.


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