Understand the
3-bit adder/subtractor in 2's complement:
Addition/Subtraction of 2's complement signed
binary numbers: When
the control bit is switched to '1', A XOR 1 = A not, so A is inverted,
and plus 1 (at cin), which is exactly the 2's complement of A, the
system will perform 'B+(-A)', which is 'B-A'; when the control bit is
switched to '0', A XOR 0 = A, and cin=0, the system will
perform 'B+A'.
Overflow:
As the definition of 'overflow', if you have negtive + negative =
positive, or positive + positive = negative, then the result of the
addition is out of range, you need an extra bit to represent the
result. The overflow indicator will show you when do you need to count
an extra bit.
Your code should be able to tell FPGA what is the extra bit in order to
display the correct corresponding decimal number.
For all the following three steps, show the code, explanation, and video demonstration.
Week 1:
Step 1: (30 points)
Use switches as the 3-bit inputs, use 'leds' to show the binary
results.
Step 2: (30 points)
Use
switches as the 3-bit inputs, use seven-segment displays to show the
decimal result, make sure have the 'minus' sign in front of the decimal
number if the result is negative.
Week 2:
Step 3: (40 points)
Use Serial In Parallel Out (SIPO) to input two 3-bit numbers [2:0] A,
and [2:0] B, into the registers, then use one switch to trigger the
computation.
