
208 THE x86 MICROPROCESSORS
6.2 | Clock
It has been mentioned that all activities on the system bus is synchronized by the system clock
which provides the basic timing. Now, what are the activities on the bus?
Let us list it out.
Reading from memory / IOi)
Writing to memory / IOii)
ese are obviously two fundamental bus activities. Depending on the type of activity, diff erent
control signals are activated. Any read or write cycle is called a bus cycle. For 8086, a bus cycle
takes 4 T states, where one T state is defi ned as the ‘period’ of the clock. If the clock frequency is
10 MHz, one T state = 0.1 m secs or 100 nsecs. A bus cycle is also ...