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 232 possible instructions

The Z80 is an older 8 bit microprocessor with a simpler instruction set

e.g. 10000111 is the instruction to double the number held in the CPU

Memory

Address DataA12 – A0 Hex I/O7-I/O0 Hex

0000000000000 0000 10100111 A7

0000000000001 0001 00111111 3F

0000000000010 0002 10000100 84

0000000000011 0003 01010101 55

0000000000100 0004 10010001 91

0000000000101 0005 00000010 02

0000000000110 0006 10111010 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