Functional Description

8-bit Fixed-point Accumulator-based ALU: SNOWBALL is a fixed point ALU capable of calculating Arithmetic and Logical Functions and No OPs.

The Arithmetic functions are as follows:

  • 2's complement addition
  • Fixed point positive number square root    (Note: taking the square root of a negative number returns an imaginary, which SNOWBALL doesn't allow.)

    The Logical Functions are:

  • AND (bitwise)
  • OR (bitwise)
  • NOT (bitwise)

    The pin usage is as follows:

  • 8 pins for data input
  • 8 pins for data output
  • 3 pins for the OP code input
  • 1 pin for the PLA reset
  • 4 pins for outputting the PLA State Bits.
  • 24 pins total used.

    SNOWBALL uses approximately 2000 x 2800 lambda of the chip.

    Division of Labor
    Segment Done By
    Cell design
    PLA Everyone
    Bus layout Everyone
    Square Root Todd and Abhinav
    T-gate Todd
    Adder Todd
    Register Todd and Indra
    AND Todd and Indra
    OR Indra
    NOT Indra
    Web Page Work Indra and Abhinav

    References

    1. Elec 422 Course Handouts, Joseph Cavallaro.
    2. Elec 422 Course Manual, Joseph Cavallaro.
    3. Streetman, Ben G., Solid State Electronic Devices, Prentice Hall, Fourth Edition, 1995.
    4. Wakerly, John F., Digital Design Principle & Practices, Prentice Hall, Second Edition, 1994.

    Comments on the CAD tools

    Although MAGIC proved usable, the circuit layout tools were not straightforward. IRSIM, on the other hand, proved lacking in a number of features found in most commercial VLSI/VHDL simulators currently. Most notable was it's inability to work well with vectors or arrays, lacking Hex or even Octal inputs and not allowing output vectors to be expanded into their components so that individual bits can be easily analyzed. SPICE also could benefit from a modern user interface, as it is irritating to have to run spice multiple times trying to isolate the proper time interval- SPICE seems more like a module used in a larger program than a program intended for direct use. SPICE's inability to convert label<->number is further evidence of this, and lastly, it's built-in plotter is nearly impossible to read more than two lines on, and even difficult at that number.