1.1.1 structure and function of processor
What does control unit do (4)
Coordinates all activities of the CPU.
Directs flow of data between the CPU and other devices.
Accepts the next instruction, decodes it, handles its execution, and stores the resulting data back in memory or registers.
Sends memory read and write requests to main memory on the control bus, as well as other command and control signals such as bus requests, bus grants, interrupt requests, etc
what does program counter do
Holds the address of the next instruction to be executed.
This could be: o the next instruction in a sequence of instructions;
the address to jump to if the current instruction is a command to jump or branch
Has a very close relationship with the memory address register.
At the start of every new fetch-decodeexecute cycle, the address held in the PC is copied to the MAR.
what does the memory address register do
This holds the address of the
memory location from which:
o data; or
o an instruction
is to be fetched or to which data is to
be written
Sends these address to memory down the address bus
what does memory data reigster do
Used to temporarily store the data
which is:
o read from; or
o written to memory.
Sometimes known as the memory buffer register (MBR) and often nicknamed the “gateway to the processor
All data to and from memory must travel down the data bus and pass through the MDR
what does current instruction register do
Holds the current instruction being
executed
The contents of the MDR are copied to the CIR if it is an instruction.
Instruction = opcode + operand
what does alu do
Performs arithmetic and logical
operations on data
Arithmetic operations on fixed and floating point numbers
Bitwise shift operations left and right.
what does accumulator do
One of a number of general-purpose
registers that modern CPUs have
Data or control information is often stored in them.
A CPU may have many generalpurposes registers for storing temporary data while instructions or calculations are being carried out.
The results of calculations carried out by the ALU can be temporarily stored here
Name 3 types of busses
Address, data, control
what does address bus do
Carries memory
addresses that identify where the
data is being read from or written to.
what does data bus do
Carries the binary 1s and
0s that make up the actual
information being transmitted
around the CPU/computer
what does control bus do
Carries command and
control signals to and from every
other component of the
CPU/computer