The cpu can
put a binary number on the address bus, to select an individual register
in the rom or ram or the i/o.
The arrows on
this bus show that addresses go one way only.
Data at the selected
address can be put on the data bus.
The cpu can
also put data on this bus which can be written into a register of ram or
i/o.
It is not possible
to write data into rom (read only memory).
This is shown
by the single arrow on the rom data bus and double arrows on the other
two.
The control bus
instructs the chips to do various things, such as when to read or write
etc.
The clock tells
all the chips when to change what they are doing.
Like the drill
sergeant who shouts "LEFT, RIGHT, LEFT, RIGHT".
The crystal
control the speed of operation.
In simple systems
the crystal frequency is 1,000,000 Hz. |
