Computer architecture Microprocessor based computers

von Neuman architecture

Clock Clock is an astable producing a square wave Synchronises processes Sets the speed of operation of CPU For most microprocessors each instruction takes several clock cycles Clock usually based around quartz crystal for accurate clock speed

CPU – Central Processing Unit Controls the movement of information around the system Performs logical and arithmetic operations Process depends on instructions fetched from memory Microprocessor is a CPU on one chip Instructions are in machine code (binary) Instructions are different for each microprocessor family

Instruction sets The Intel Pentium 4 instruction set is enormous, it is a 32 bit data bus so there are 2 32 possible instructionsPentium 4 instruction set The Z80 is an older 8 bit microprocessor with a simpler instruction setinstruction set e.g is the instruction to double the number held in the CPU

Memory AddressData A 12 – A 0 HexI/O 7 -I/O 0 Hex A F BA Continued…

ROM – Read Only Memory Permanent store Information cannot be changed Information does not disappear when power turned off Used for storing programs so that machine has program to start at turn on

RAM - Random Access Memory Temporary store Data can be written to or read from RAM Information is lost when power is turned off (volatile)

Input port Obtains in formation from outside the system in digital form

Output port Sends digital information to outside the  P system Information is latched so stays at output until changed

Data bus Set of wires (8 in 8 bit system) Two way - carry data to and from  P All devices connected to same bus (omnibus means for all)

Address bus Set of wires Provides information about which device to write to or read from Provides address in memory being written to or read from

Control bus Set of wires Provides information about direction of data movement Can provide information about device being addressed (memory, I/O) Can provide timing information