1 (479)

Prévia do material em texto

Step 1 of 3 9.016E Consider the design of a 16 bit full adder/subtracter with mode control, carry input, carry output, and two's complement overflow output. The circuit consists of two 16 bit inputs along with carry input and mode control input. The total number of input bits required is shown in Table 1 as follows: Table 1 Augend/ Minuend bits 16 Addend/ Subtrahend bits 16 Carry input bit 1 Mode control bit 1 Total bits 34 Total number of input bits required is 34 bits. Step 2 of 3 The output consists of 16 bit adder/subtracter result, carry output and two's complement overflow output. Consider carry output and overflow output as a single common bit. During the circuit operated as adder, the common bit is treated as carry output bit. During the circuit operated as subtracter, the common bit is treated as two's complement over flow output. The subtraction operation is performed as an addition operation of minuend and the two's complement of subtrahend. The total number of output bits required is shown in Table 2 as follows: Table 2 Result 16 Carry/Two's complement 1 Overflow output Total bits 17 The total number of output bits required is 17 bits. Step 3 of 3 The Read only memory is designated as Here n is number of input bits, m is number of output bits. The input bits are address bits and output bits are data bits. The address bits are called ROM bits. Therefore, the number of address bits required for the circuit are 34 The number of data bits are 17 The size of the ROM required is as follows: Size of the ROM = x17 Therefore, the number of ROM bits are 34