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  • Author Author: baldengineer
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Are you still using 7400-Series Logic, if so, where?

baldengineer

Over the past several months, I have been learning about and repairing 8-bit computer and video game systems. So far, I have worked on the VIC-20, C64, ZX-81, Apple II, and have been learning about the TI 99/A.

 

It always amazes how much of these early computer systems were built almost entirely with standard 7400-series (LS and HC) chips.

 

Occasionally, I need to replace a 7400-series chip. (I always hope it is one of those and not one of the ASICs!) While looking for modern replacements, I have noticed the trend that they are becoming more scarce. The LS-series is almost entirely gone--and with good reason. While HC and HCT continue to be somewhat available, they are usually only available in surface-mount packages.

 

That leads me to the question: Who is still using the venerable 7400-series logic chips today?

 

To me, there are three groups that might be using them:

  1. Learning. Students and hobbyist learning about digital logic
  2. New Design. Hardware that needs glue-logic. Are these using multi-gate chips or the single-gate variants?
  3. Repair. Older electronics in need of replacements. Here is where I mostly sit.

 

Do you fit into one of those categories? If not, where do you land?

 

And THEN, which chips are the must-have on-hand?

Obviously, the answer depends on how you might be using them. But, I'm curious to know how you use 7400-series chips and which ones would you keep in stock?

  • in reply to ajcc

    Thank you for a great example and the sales brochure! I definitely didn't want to sound like there is no place for logic chips, just that they are more and more integrated to save board space and cost.

     

    It is not 100 % related, but there is also a TI's app note / brochure that suggested replacing all other small chips with their MSP430 - for example various timers, slow logic circuits, debouncers for buttons etc. The goal is to have fewer unique parts on a BOM (even more that one piece). I just can't find it right now.

  • in reply to koudelad

    You might just not have seen them, as an example and because it's right next to me, there are a handful of 74-series logic ICs on the BeagleBone Black. The BBB is open source hardware so the full schematic is available for download.

     


    Green ring is a SN74LVC1G07 Single Buffer/Driver With Open-Drain Output
    Red ring is a SN74LVC1G06 Single Inverter Buffer/Driver With Open-Drain Outputimage

     

    image

    Yellow ring is a SN74AUC1G74 Single Positive-Edge-Triggered D-Type Flip-Flop with Clear and Preset

    Blue ring is a SN74LVC2G241 Dual Buffer and Driver With 3-State Outputs

     

    Now the packages doesn't say 74-something on them, instead they have catchy names like cf5, CV5 or C14b.

     

    While searching for the parts I even found a nice sales brochure from Texas Instrument that talks about how their Little Logic ICs can be used in modern applications.

  • I just used a couple of 4000 series logic chips in the Pong game that I rebuilt.  And I have an assortment of 74 and 74LS (even some 54 mil grade parts) from the late 70s and early 80s when I did a lot of prototyping.  I even have early 555s from 1972.  And I have a bunch of early op-amps (709, 741, 747) from the 70s.  A lot of them in ceramic packages and hand marked because we used to hand screen them for better than spec performance.

     

    The most interesting thing I found that I had forgotten that I had is a National Semi MM5738 8-digit algebraic 5 function calculator chip.  Might be a fun retro build for later.

  • in reply to baldengineer

    Oops!  Yes that was a typo.  I meant to type 74HC4066D.  The CD4066B is a pin compatible part, but with a higher voltage range (20V versus 10V Max Vcc and input).

  • in reply to baldengineer

    4000 series had equivalent logic functions to 7400 but usually different pinout. 74C series retained the 7400 pinouts but used CMOS logic levels and voltages. Each series had some unique parts. I like 4000, 4500 and 74C series parts because they were much lower power and operated over a much wider range of voltages. 4000 series parts were not quite as fast as LS or S parts. One of the parts I used a lot and sill use is a 4040 ripple counter. Another would be 40106 which is equivalent to a 74C14 hex Schmitt trigger inverter. It is funny how I can still remember the logic function of many part numbers.