TTL Turns 50

Ed Grochowski

Introduction

Here is an article that made my heart glow:

Fifty years of TTL

Transistor-transistor logic (TTL) is the same age that I am. I have fond memories of designing, building, and debugging TTL projects when I was a teenager. I even designed and built a home security system using TTL as recently as 2002.

I still have on my bookshelf the Texas Instruments "TTL Data Book" pictured above. It sits next to Signetics' "Integrated Circuits" and Intel's "Component Data Catalog" from the same timeframe (1974 and 1978, respectively).

You are probably wondering in an age of billion-transistor chips, how much use is there for chips containing tens or hundreds of transistors? TTL is still manufactured and used today as "glue logic" - connecting billion-transistor chips may still require TTL decoders and transceivers. A trivial task like ANDing together two signals is best done by a 74LS08 TTL chip. The main obstacles to using TTL are relatively high voltage (5 volts, although 3.3 volt families are available) and glacial (5-15ns) propagation delays.

The longevity of TTL is a result of its "building block" approach. TTL chips do not do much by themselves - a typical TTL chip might contain four 2-input NAND gates, a 4-bit counter, a 3-8 decoder, four 2-1 multiplexers, an 8-bit shift register, or an 8-bit transceiver. The power comes from putting together tens or hundreds of TTL chips to create complex systems. TTL is like Tinkertoys - a bucket of parts that one can assemble into anything one imagines. Modularity and interoperability go a long way.