The Clock Generator

The clock generator in MacBreadboard can operate in one of four 
modes.  The modes are selectable from the 'Clock' menu, and 
identifiable by a check mark in the menu and a unique picture on 
the trainer.  Typical frequencies generated are 10Hz and lower.

•	Free-Run -	a continuous square wave signal is generated.  
		The frequency is adjustable by sliding the simulated control 
		right or left.

•	Positive pulse -	In this mode, a button is shown in the clock 
		function area of the trainer.  Pressing the button causes a 
		clock 'pulse' to be generated.  The pulse is initially low, then 
		it goes high and finally it returns low again.  The frequency
		is determined by the Free-Run clock's setting.  A step function
		may be simulated by pressing and holding the mouse button.  
		When the button is released, the clock output returns to its 
		initial state.

•	Negative pulse -	Similar to the positive pulse except that the
		initial and final states of the clock are HIGH, not low.

•	Step -	Or half pulse.  Clicking on the step button generates 
		a state change in the clock.  If it was HIGH, it is now LOW 			
		and vice-versa.  (Holding the mouse button down has no effect 
		in step mode.)