Well we have looked at the uses of the data and address buses, but as some of you have noticed I have not talked about the control bus. For those that were at the open days it might be worth while looking through the blog at older entries.

The control bus is different from the other two buses in being a group of discrete wires with separate functions.

• Read – signals a memory read operation is to take place
• Write – signals a memory write operation is to take place
• Clock – synchronises the signals being passed in and out of the processor
• Reset – clears all registers and buses of data
• Interrupt – tells the processor to save current process, run interrupt process until completed, then resume its activities (can be ignored)
• Non Maskable Interrupt (NMI) – tells the processor to save current process, run interrupt process until completed, then resume its activities (cannot be ignored)

So as you can see these functions are all separate but are controls and are therefore grouped into the control bus.