8155 Control Register

D7	D6	D5	D4	D3	D2	D1	D0
Timer command		IEB	IEA	PC (ALT1 and ALT0)		PB	PA

Control register also called command register.
It is a 8-bit which defines different functions.
It defines the function of different ports such as input, output or handshaking mode.
It also defines timer command for timer to start and stop.

Timer command:

00 -No effect
01 -Stop counting if timer is running. No operation if counter is not running.
10 -Stop after terminal counter is reached.
11 -Start timer if timer is not running. If timer is running reload the TC and then continue.


Interrupt Enable for PA and PB(D4 and D5):

1- enable
0- disable

Input or output for PA and PB respectively:

1-output
0-input