Detailed Question: this assignment need to build 16 bit cpu in logisim
Description
For your final project, you will put together all that you have learned to design the simplest CPU that can do something slightly interesting. It will execute a small set of 16-bit instructions, of two formats:
R-type:
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opcode (4-bits)
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RS (2-bits)
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RT (2-bits)
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RD (2-bits)
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Unused (6-bits) 000000
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15
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0
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I-type (includes jump):
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opcode (4-bits)
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RS (2-bits)
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RT (2-bits)
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Immediate (8-bits)
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15
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Registers
There will be four 8-bit registers: $R0, $R1, $R2, and $R3. $R0 is always zero. The rest will hold readable and writeable data.
Instructions
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Opcode
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Instruction
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Action
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0000
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add $RD, $RS, $RT
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$RD = $RS + $RT
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0001
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sub $RD, $RS, $RT
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$RD = $RS - $RT
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0010
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slt $RD, $RS, $RT
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$RD = $RS < $RT
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0011
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bne $RS, $RT, Immediate
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If $RS!=$RT then $PC=$PC+2+Immediate<<1
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0100
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addi $RT, $RS, Immediate
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$RT = $RS + Immediate
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0101
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beq $RS, $RT, Immediate
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If $RS==$RT then $PC=$PC+2+Immediate<<1
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0110
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nand $RD, $RS, $RT
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$RD = !($RS && $RT)
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0111
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UNUSED
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1000
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sb $RT, Immediate($RS)
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Memory[$RS + Immediate] = $RT
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1001
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UNUSED
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1010
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UNUSED
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1011
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j Immediate
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$PC = Immediate
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1100
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lb $RT, Immediate($RS)
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$RT = Memory[$RS + Immediate]
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1101
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rand $RT, $RS
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$RT = random number [0, $RS-1]
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1110
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disp $RS
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Display $RS on the 2 digit hex display
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1111
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halt
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Stops the CPU
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Circuit Implementation
As with large programs, designing a large circuit should be done in small, manageable chunks. You will want to create a subcircuit for the major parts such as the register file, control, and ALU.
Clock
The most important part of your circuit is a clock element. It will be wired into each of the state elements (Instruction Memory, Register File, Data Memory) to trigger an update.
The halt instruction should block the clock output from reaching the state elements which will effectively stop the CPU from running.
Instruction Memory
For instruction memory, we will use ROM. It will be 8-bit addressable and hold 16-bit data words (our instructions). You can edit the contents of the ROM using the pointer tool and typing hexadecimal numbers or by right clicking the ROM and saying edit or load... I hope to have an assembler for you soon, but in the meantime, you can assemble them by hand. Once you do that, you may save programs you have input and load them later. I will provide a few sample programs to test your CPU with.
The output of the ROM is an instruction. You can either use a bunch of splitters to extract the right bits and recombine them (for opcode, registers, immediate, etc.) or you can use a bit selector component in logisim. For instance, a bit selector with output bits set to 4 and the selection input of 3 (use a constant element in logisim) will select the 3rd group of 4-bits from the instruction word. Since it is zero-indexed, this means the highest order group of 4 bits, which is our opcode.
Data Memory
Data memory will be a RAM component. Use an 8-bit address and 8-bit data.
Requirements
By the due date, you need to submit:
· Your circuit file from logisim with at least the ALU, Register file, and control as subcircuits.
· 2 different programs that run on your CPU written in assembly.
· The machine code version of the 2 programs above saved from the ROM component in logisim.
http://people.cs.pitt.edu/~jmisurda/teaching/cs447/ApAsm.htm