Timing and control unit

Timing and control unit : 

           It provides timing and control signal to the microprocessor to perform the various operation.It has three control signal. It controls all external and internal circuits. It operates with reference to clock signal.It synchronizes all the data transfers.

           The three control signals are:-

1. ALE-Airthmetic Latch Enable, It provides control signal to synchronize the components of microprocessor.
2. WR-This is used for writing operation.This is active low.
3. RD- This is  used for reading operation. This is active low

There are three status signal used in microprocessor S0, S1 and IO/M. It changes its status according the provided input to these pins. Below is the truth table for various combinations of status signals.

      

IO/M (Active Low)	S1	S2	Data bus status (Output)
0	0	0	Halt
0	0	1	Memory Write
0	1	0	Memory read
1	0	1	IO write
1	1	0	IO read
0	1	1	Opcode fetch
1	1	1	Interrupt Acknowledge