Consider a CPU with an 18-bit data bus and a 26-bit address bus. a) How many byt
ID: 3742930 • Letter: C
Question
Consider a CPU with an 18-bit data bus and a 26-bit address bus.a) How many bytes of memory can be accessed? b) How wide (in bits) would you expect most of the CPU’s registers to be? c) How wide (in bits) is the Program Counter? d) How wide (in bits) is the Instruction Register? e) How wide (in bits) is the Data Address Register? f) How wide (in bits) is the Data-In Register? g) How wide (in bits) is the Data-Out Register? Consider a CPU with an 18-bit data bus and a 26-bit address bus.
a) How many bytes of memory can be accessed? b) How wide (in bits) would you expect most of the CPU’s registers to be? c) How wide (in bits) is the Program Counter? d) How wide (in bits) is the Instruction Register? e) How wide (in bits) is the Data Address Register? f) How wide (in bits) is the Data-In Register? g) How wide (in bits) is the Data-Out Register? Consider a CPU with an 18-bit data bus and a 26-bit address bus.
a) How many bytes of memory can be accessed? b) How wide (in bits) would you expect most of the CPU’s registers to be? c) How wide (in bits) is the Program Counter? d) How wide (in bits) is the Instruction Register? e) How wide (in bits) is the Data Address Register? f) How wide (in bits) is the Data-In Register? g) How wide (in bits) is the Data-Out Register?
Explanation / Answer
Answer
An address bus is used to specify a physical address whereas a data bus is used to read data from the memory or write data to the memory.
Given that the CPU has an 18-bit data bus and a 26-bit address bus.
a)
The total byte of memory that can be accessed will depend on the address bus.
As the CPU has 26-bit address bus, we can have 226 unique combinations of addresses.
By convention, each address points to 1 byte of data.
Hence, 226 bytes of memory can be accessed.
b)
As the data bus size is 18 bits, we expect most of the CPU’s registers to be 18 bits.
c)
The program counter stores the address of the next instruction.
As it stores the address, it is of size 26 bits.
d)
The Instruction Register holds the instruction currently being executed or decoded.
The Instruction Register size will depend on the size of the instructions.
As the data bus size is 18 bits, the Instruction Register will be 16 bits.
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