MCP23008 IO Expander - Demultiplexer

DeMUX buffer offline by hand testing notes

http://www.blogger.com/blogger.g?blogID=1840459474737789074#editor/target=post;postID=9217466016179799052

Now I have done the following test.

1. Shorted all HC573 inputs using jumpers.  In other words, I am testing all 8 bits in one go.  At first I thought I should test one bit by one bit, but then I found the floating high impedance problem causes the LED lighting confusing.

2. I tested OE and LE at the same time, connecting them to 5V0 and Gnd, while the input is connected to 5V0 and Gnd.  I tried all the combinations, high/low for OE, LE, input and found the output enble, latch enable are behaving as what I expected.

So far so good.  Next step is to check out my NOR gate based demux switch on/off idea.

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