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The 7400 series is a community of digital logic integrated circuits. They were originally based on Transistor Transistor Logic (TTL) but the newer versions are CMOS. Most common logic functions, gates, buffers, registers etc, are available in the 7400s.

7400 logic comes in a number of flavours, the most historically popular are:

  • 74xx - The original TTL based 7400 family. They were slow and used a fair amount of power.
  • 74Sxx - The first schottky transistor based family. It was optimised for speed, and used a moderate amount of power.
  • 74LSxx - Using the same technology as the 74Sxx family, the 74LSxx family are optimised for low power consumption. 74LS are in very common usage and are easy to obtain.
  • 74Cxx - An attempt to implement 7400 series logic with CMOS rather than TTL technology. Relatively unsuccessful, this family has been largely replaced by the 74HCxx and 74HCTxx families. The 74C and 74HC families is not signal level compatible with the TTL series.
  • 74HCxx - Based on a polysilicon rather than metal gate structure, this CMOS based family is faster and uses less power than the 74Cxx family. The HC stands for High speed CMOS but this family is still slower than the 74LS and 74S families. This family is probably the most widely available.
  • 74HCTxx - Based on the same technology as the 74HCxx series, this family uses the same signal levels as the TTL based families.
Several other families of 7400 ICs exist, such as the 74F (fast) and and 74H (slightly faster than 7400) families. If you want to learn how to work with these chips then take a look at Pin-outs for 7400 chips.

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