The current processor has only one 8-bit external output interface which can be

Question

The current processor has only one 8-bit external output interface which can be written to with the 'out' instruction. Microcontrollers tend to have much more bits on their output interfaces. Provide a detailed explanation and justification of how the UoS educational processor could be modified to have four 8-bit output ports instead of one.

In particular:

i) explain what should be changed in the encoding of the 'out' instruction to enable four output ports; provide the new instruction encoding and give examples of this encoding;

ii) explain what should be changed in the part dealing with the external interface in cpu.vhd to have 4 output ports which can be written to with the newly defined encoding of the 'out' instruction;

iii) explain what should be changed in the port declaration of the cpu entity in cpu.vhd.

Explanation / Answer

i) Declare port has four variables as pin numbers.

eg. Port A (a,b,c,d )

Out Port A

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