Datapath

Datapath: flow of data during instruction execution

Fig. 5.1

Process

PC gives address of next instruction to (instruction) memory

Memory gives instruction contents to IR (instruction register, not shown)

IR gives

Register numbers (2 source, 1 destination) to registers

Immediate data to ALU

Registers give data to

ALU

(Data) memory

ALU processes operands and gives result to

Register (arithmetic/logical result)

Memory (as data address for load or store)

Data memory gives data to registers (if load)

What's missing from this picture?

How to update the PC?

Could have counter to increment, but what about branches and jumps?

Use ALU to compute branch address, but need more control

Where do register addresses come from?

How do we control register read/write?

What about immediate operands?

How to determine what operation for ALU to perform?