The last stage in building the ALU is to combine the NOT/NEG and the AND/ADD subcircuits as shown in Figure 7 to create the complete ALU. NOTINEG ANDIADD CRY NOTINEG Pass Cout OF -Invert Q Figure 7. The complete ALU This ALU contains three input control signals: The / Invert signal, when active, indicates that some type of inversion, either a one's or two's complement is taking place. The A Only signal, when active, indicates that only the A operand is being acted upon by the ALU. . . . The Logic/Arith signal operates so that when Logic/Arith 0, an arithmetic operation is performed When Logic/ Arith -1, a logical operation is performed by the ALLU Once this notation is understood, you may be able to fill out the function definition table in Table 3 for this circuit even without reference to Figure 7. Consider the example filled-in in Table 3 /"A-Only-1 implies that the A and B operands are combined in some fashion. . Invert 1 implies that A is not inverted (neither a one's nor a two's complement is performed.) Logic/Arith 0 implies the operation is arithmetic. The only two-operand, noninverting arithmetic operation of which our ALU is capable is the sum, AB Table 3. ALU function definition table A On 0 0 ic/Arith Function 0 0 0 0 0 Arithmetic Sum, A+B The last stage in building the ALU is to combine the NOT/NEG and the AND/ADD subcircuits as shown in Figure 7 to create the complete ALU. NOTINEG ANDIADD CRY NOTINEG Pass Cout OF -Invert Q Figure 7. The complete ALU This ALU contains three input control signals: The / Invert signal, when active, indicates that some type of inversion, either a one's or two's complement is taking place. The A Only signal, when active, indicates that only the A operand is being acted upon by the ALU. . . . The Logic/Arith signal operates so that when Logic/Arith 0, an arithmetic operation is performed When Logic/ Arith -1, a logical operation is performed by the ALLU Once this notation is understood, you may be able to fill out the function definition table in Table 3 for this circuit even without reference to Figure 7. Consider the example filled-in in Table 3 /"A-Only-1 implies that the A and B operands are combined in some fashion. . Invert 1 implies that A is not inverted (neither a one's nor a two's complement is performed.) Logic/Arith 0 implies the operation is arithmetic. The only two-operand, noninverting arithmetic operation of which our ALU is capable is the sum, AB Table 3. ALU function definition table A On 0 0 ic/Arith Function 0 0 0 0 0 Arithmetic Sum, A+B
