I came across this question in my homework:

Implement the following gates using only one TTL IC: one inverter, one 2-input NAND and one 3-input NAND.

The type of IC they're talking about has 14 pins, where pins 7 and 14 are GND and Vcc respectively. Also, the rest of the pins are the in/outputs of 4 gates of the same type.

This example is given:

Using only one TTL IC (OR gates) to implement a 4-input OR gate.

This is the type of IC they're talking about.

So far, I can only figure out the following:

  1. The gates inside the IC should be NAND.
  2. 1 NAND gate can be used to make the inverter: NAND as inverter
  3. 1 NAND gate as the 2-input NAND (obviously).
  4. 3 NAND gates can be used as the 3-input NAND: 3-input NAND using three 2-input NANDS

However, there are not enough NAND gates inside the IC for all of this. How do I fit them all?


1 Answer 1


Well, obviously, a triple 3-input NAND gate (74LS10), with various unneeded inputs tied high, will meet the stated requirements.

  • \$\begingroup\$ I'm really new to this, so I don't know what "TTL IC" actually means. Is it like a family of ICs with names in a particular form, e.g. "74XXXX"? \$\endgroup\$
    – Vero
    Sep 28, 2019 at 15:08
  • \$\begingroup\$ Yes, exactly. What kind of course is this, that this wasn't explained to you at the beginning? Of course, this kind of knowledge is of limited value today. Nobody designs with this stuff any more, except for the retrocomputing folks. I did my last serious work with SSI/MSI in the late 1980s. \$\endgroup\$
    – Dave Tweed
    Sep 28, 2019 at 15:10
  • \$\begingroup\$ @DaveTweed -- knowing your SSI/MSI is still useful for "glue" functions though \$\endgroup\$ Sep 28, 2019 at 15:23
  • \$\begingroup\$ @ThreePhaseEel: Even then, such functions are more likely to be buried in a nearby CPLD or FPGA. In a pinch, use one of those SOT23-6 "single gate" packages. \$\endgroup\$
    – Dave Tweed
    Sep 28, 2019 at 15:25

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