Some progress and a binary tutorial

Ok, while waiting for the hardware to arrive, i’ve made some progress.

DSCF1038

I had a comment regarding my schematics and how come both the left MUX, the right MUX and the LCD are all connected to the same wires in the LPT port. Is that gonna work?

Yes it will, it’s all down to binary numbers and how computers “talk” to different chips on the same wires (in parallel). It’s called a databus.

But if they are all on the same wires, won’t there be collisions? No, because we have something called a chip select (CS or E signal).

All the chips listen to the same bussignals in parallel but only the chip that receives the chip select signal will use the data on the bus and the A/D converter and the LCD have their chip select on different lines.

There was also a question about how an Inverter can be used to select between the left and the right MUX.

A value of 0-15 are represented with 4 binary digits (A0-A3 in the schematics)  so we can use that to select one of 16 inputs in both multiplexers in parallel.

What happens when we output the number 16? Well the 5th line goes to a logic 1. This means that the left MUX will be disabled because the E input of the MUX needs to be a logic 0 (or off) for the MUX to let anything through. So by putting out the number 16-31, the left MUX will disconnect but at the same time the Inverter will “Invert” that logic 1 to a logic 0 so that the right MUX will put it’s voltages through instead.

This means that from 0-15 the left MUX delivers and from 16-31 the right MUX takes over. Easy or what 🙂

Then for you that understands exactly how it works also know that when putting out values to the LCD the MUXing will jump around like crazy but that doesn’t really matter as we are not reading any values from the A/D converter because it’s chip select line is off.

I know this is technical but if you build it like this there will be a minimum of wires to connect and it will just be a matter of putting out the right values to the LPT port.

/Jan

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One Response to “Some progress and a binary tutorial”

  1. fabrizio Says:

    Fantastic!
    Now all is clear, thanks!

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