Limitations:
This trainer is suitable for instructional purposes.  The following 
			'real world' parameters are ignored:

	•  fan-out - a typical TTL gate output can only drive three to five
			other TTL inputs.  In this version, gate outputs can be 
			connected to an unlimited number of inputs.
	•  LEDs can be assumed to have an internal resistor which limits 
			the maximum current flow through them.  In this  simulation, 
			you can connect an LED directly to the +5 volt input.  If a 
			current limiting resistor were not used, excessive current 
			would damage (fry/smoke) the LED.
	•  Timing diagrams can be used for a relative comparison of 
			signals.  Changes in dip switches, for example, are centered 
			within the clock pulse where they occured.  No real-time 
			information is provided.  The timing diagrams are an accurate 
			first approximation.  Parameters such as propogation delay, 
			and set up times are ignored in this version of MacBreadboard.
	•  Feedback loops (ie tying a gates output to one of it's inputs)
			is generally allowed, but only relative timing information can 
			be provided for asynchronous gates.