Tiny url http://tinyurl.com/jdp3qqr

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• using the NAND gates, then if that was successful, try
• a decode chip from the same family.
• Combining a Single 3-Input Positive AND-OR Gate and a single decode chip to make a high speed 74139.

  The Z88 only uses one half of the dual functionality of the full chip.
  Using just NAND gates requires too many of them. However using the Single 3-Input Positive AND-OR Gate and a single decode chip allows this device to be built with four 3mm high speed chips.

• See http://www.neuroproductions.be/logic-lab/index.php?id=63191 for the ongoing logic in checking that the full chip will work. 

Choosing a Fast NAND gate

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The Z88 only uses one half of this dual decode chip. This circuit may be made with

• 3 inverters
• 2 NAND gates

The inverters are slower than the NAND gates, so it was decided to use 5 NAND gates using 3 of the gates as inverters.

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Circuit updated 15:04 6/9/16

Can a Full 74139 chip be built?

The Z88 only uses one half of the dual functionality of the full chip.

Using just NAND gates requires too many of them. See http://www.neuroproductions.be/logic-lab/index.php?id=63191 for the unfinished work in getting a full chip to work.

Building a prototype board internally

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Circuit Diagram using the Single 3-Input Positive AND-OR Gate and a single decode chip.

To be drawn

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