a) Design an expanding opcode instruction set for a comupter having 15-bit instr
ID: 3869766 • Letter: A
Question
a) Design an expanding opcode instruction set for a comupter having 15-bit instructions and the following types of instructions. There are 16 CPU registers and 8 bit addresses
i. seven instructions with three registers
ii. seven instructions with one address value
iii. eight instructions with one register
b) Design an expanding opcode encoding for a computer with uniform length 24 bit instructions. The instruction set is organized into three categories (T1, T2, and T3). The CPU has 16 general purpose registers, addresses are 10 bits long, and there is 8-bit data.
i. T1: 63 instructions, each refers to two CPU registers and includes one address
ii. T2: 30 instructions, each refers to one CPU register and includes an immediate data value
iii. T3: 32 instructions, each referst to two CPU registers
iv. For each type draw how the various instruction fields could be assigned. Indicate the number of bits in each field and point out any unused bit fields.
Explanation / Answer
a) 15 bit instructions
16 CPU instructions= 24 , max 4 bits
8 bit address
i.
unused bits = 15 - 6 = 9 bits
ii.
unused = 15 - 11 = 8 bits
iii.
unused = 15 - 4 = 9 bits
b) 24 bits instructions
16 general purpose registers , needs 4 bits
10 bit address
8 bit data
i.T1
unused = 24 - 17 = 7 bits
ii. T2:
unused = 24 - 14 = 10 bits
iii. T3
unused = 24 - 6 = 18 bits
Opcode = 3 bits Register = 3bitsRelated Questions
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