Consider a hypothetical microprocessor generating a 16-bit address (for example,

Question

Consider a hypothetical microprocessor generating a 16-bit address (for example, assume that the program counter and the address register are 16bits wide) and having a 16-bit Data Bus.
A. What is the maximum memory address space that the processor can access directly if it is connected to a “16-bit memory”?
B. What is the maximum memory address space that the processor can access directly if it is connected to an “8-bit memory”?
C. What architectural features will allow this microprocessor to access a separate “I/O Space”?
D. If an input and an output instruction can specify an 8-bit I/O port number, how many 8-bit I/O ports can the microprocessor support? How many 16-bit I/O ports? Explain.

Explanation / Answer

Questions are kind of ambiguous as "16-bit memory" and "8-bit memory" could mean a number of different things, however I'll assume they refer to the amount of memory responding to each "address". A 16-bit address bus means the micro can generate 64K (65,536) different addresses, so A) The address space is 65,536 * 16-bits, so 1024K bits, 64K 16-bit words, or 128K bytes. B) 65536 * 8-bits = 512K bits, or 64K bytes C) The controller needs a separate address bus for the I/O space (similar to the x86 family) and either instructions specifically for reading and writing that address space (inp and outp for example) or special addressing modes for the standard instructions. D) again, an 8-bit I/O bus allows 256 separate addresses. so either 256 8-bit or 256 16-bit ports.

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