The Sign Extender

Data Memory

In addition to instruction memory, we need data memory.

Now in reality, memory is memory, so when we say Data memory, we simply mean we a to need path the single computer working memory to load/store data in load/store instructions.

We color code data memory blue, like instruction memory, to remind us that it is the same memory, only accessed along a different path or bus.


Fig.3.5 Data Memory


We know that many instructions have immediate parts that are 16 bits in length.

The immediate is added to a 32-bit operand (register or PC contents) to create an operand or perhaps a new address, for instance in a branch instruction.

Since the immediate may be + or ─, then to add it to a 32-bit argument, we must sign extend it to 32-bits.

The sign extension unit performs this function.


Fig.3.6 Sign Extender


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ALU Architecture for Processing | Branch Instructions

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