THE BOMB! -- PART 2

Indestructible This Time!

FUNCTIONAL DESCRIPTION

The BOMB! is a simplified ALU that has the basic functionality of a simple calculator. The chip can add, subtract, and, or, shift left, and shift right. It has two registers from which values to be performed on are loaded into. The result of the operation is not stored in a register, instead it is directly outputted on the output lines.

The chip also takes two clock inputs in order to correctly latch the inputs and outputs of the ALU.

ISSUES

The simplicity of the chip and the lack of more complex functions is a result of the very limited amount of time we had. The goal in creating this chip was to guarantee we had a working chip in as little time as possible. The chip, while simple, is completely functional.

INSTRUCTION SET SPECIFICATION

The ALU can do 6 different operations. The arithmetic and logical instructions all operate on the values in register A and register B. The shift operations only operates on the value in register B.

In order to load a value into the registers, the STREGA and STREGB signals must be toggled high. The GO signal is used to correctly latch both the inputs to the ALU as well as the outputs.

A sample sequence of operations is as follows:

  1. Drive 4-bits on pins REGA0-REGA3 and drive STREGA high.
  2. Drive 4-bits on pins REGB0-REGB3 and drive STREGB high.
  3. Drive the CTRLA, CTRLB, and CTRLC signals with the correct opcode (with CTRLC as the most significant bit, and CTRLA as the least significant bit) and drive GO high.
  4. The output of the ALU will be present on output pins OUT0-OUT3.


OPCODEINSTRUCTION DESCRIPTION
ARITHMETIC/LOGICAL
000
ADD
 ADDs the value in the register to the value on the accumulator and places the result in the accumulator
001
SUB
 SUBTRACTs the value in the register to the value on the accumulator and places the result in the accumulator
010
AND
 Performs a logical AND on the value in the register to the value on the accumulator and places the result in the accumulator
011
OR
 Performs a logical OR on the value in the register to the value on the accumulator and places the result in the accumulator
100
SL
 SHIFTS the binary value in the register to the left by one and places a zero in the LSB
101
SR
 SHIFTS the binary value in the register to the right by one and places a zero in the MSB

PAD LABELS for the final chip:



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