For some strange reason, my 10 year old son has taken an interest in digital
logic and trying to teach it to him has resulted in a LOT of circuits,
finding logic simulators and refreshing my understanding. Rather than just
doing it for him, I'm adding it to the web site for other. Possibly for
kids. Or adults. I tried my darndest to use small words.

I'd like some feedback on the first page:
http://techref.massmind.org/techref/logic/nand.htm

It makes use of LogicSim, a Java program, kindly converted to an applet, and
written by Andreas Tetzl of 
http://www.tetzl.de It is a very graphically nice presentation of switches,
LEDs, logic gates, and a binary input and output which converts from and to
decimal for easy testing of math stuff.

More to follow, possible with less explanatory text. We made (all in 4 bit
width) decoders, multiplexers, latches, memory, adders, 7 segment drivers,
multipliers, counters, presettable counter, ALU (4 functions: add, negate,
shift right or left), and a little thing that increments one number by
another on each clock cycle. 

Then LogicSim got a bit slow and we switched to LogiSim (no "c") and are
just about ready to put together a minimal 4 bit uC with a program memory,
program counter, source and destination decoders, ALU, accumulator, input
and output.

LogiSim is not as pretty and doesn't do the decimal conversions, but it is
screaming fast and supports busses and modules with many inputs and outputs.
Sadly, it can not run as an applet (as far as I can tell) so I'm not sure
how I can present our uC at the end, but hopefully either LogicSim will get
faster, or LogiSim will add that ability.

---
James Newton, massmind.org Knowledge Archiver 
james@massmind.org 1-619-652-0593 fax:1-208-279-8767 
http://www.massmind.org Saving what YOU know.

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