Difference between SN and CD prefixes in 74HC IC series

Discussion in 'General Electronics Chat' started by PauloConstantino, Sep 10, 2016.

  1. PauloConstantino

    Thread Starter Member

    Jun 23, 2016
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    Hi all,

    does anyone know the difference between the prefixes SN and CD for the 74HC series of IC's ?

    Thanks in advance.

    Paulo
     
  2. lightingman

    Senior Member

    Apr 19, 2007
    374
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    Different manufacturers.

    Daniel.
     
  3. PauloConstantino

    Thread Starter Member

    Jun 23, 2016
    121
    5
    Oh boy is that all? So why do I only see either SN or CD in all my HC chips? Only 2 manufacturers in the world ?
     
  4. crutschow

    Expert

    Mar 14, 2008
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    What's an example of a 74HC device with a CD prefix?
     
  5. absf

    Senior Member

    Dec 29, 2010
    1,492
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    Here are some with other prefixes..
    HEF74hc00.PNG
     
  6. absf

    Senior Member

    Dec 29, 2010
    1,492
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    CD was used originally by RCA for the 4000 CMOS family. After TI bought over RCA, they continue to use CD for their HC TTL chips...

    cd74hc00.PNG
    Allen
     
  7. hp1729

    Well-Known Member

    Nov 23, 2015
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    Data sheets! Read the data sheets.
     
  8. GopherT

    AAC Fanatic!

    Nov 23, 2012
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  9. crutschow

    Expert

    Mar 14, 2008
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    Okay.
    I find it curious that they mixed the old CD prefix for the original CMOS devices with the 74HC designation for the newer CMOS devices.
     
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  10. RichardO

    Well-Known Member

    May 4, 2013
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    I saw a reference someplace that TI has a different oscillator in the SN74HC4060 than the CD74HC4060. I have not verified this, however.
     
  11. cabraham

    Member

    Oct 29, 2011
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    The "CD" designation indicates pin compatibility with the older 4000 series CMOS logic family. The original TTL family came out in 1968, designated as "74xx". Around 1975, the 4000 series CMOS logic parts came out. To avoid using the wrong part, since CMOS had issues with power supply sequencing, input floating, the pin outs were intentionally made different. So a quad NAND gate in the 7400 series TTL was NOT pin compatible with a quad NAND in 4000 CMOS.

    Then when the "74HCxx" family of higher speed CMOS parts came out, the pin out was made compatible with the TTL family. Thus a 74HC00 quad NAND is pin compatible with the 7400 TTL quad NAND. But the quad NAND in 4000 CMOS logic family has a different pin out.

    In order to accommodate the 4000 CMOS pin out if a board is already designed that way, the 74HC family offers some parts with "CD4000" pin outs. That is where the difference lies. So a 74HC part with CD4000 pin out allows a user to use a new part with better performance while keeping the existing CD4000 pinout. Did I help?

    :) Claude
     
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  12. RichardO

    Well-Known Member

    May 4, 2013
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    @cabraham has good information. I would add that the pinout differences between TTL and CMOS were dealt with in the 74C00 series initially.

    A little bit of nit picking...
    It says here https://en.wikipedia.org/wiki/Logic_family#TTL that TI introduced 7400 series TTL in 1964 RCA introduced 4000 series CMOS in 1968.
    I haven't verified these dates but I do have a 1971 RCA CMOS data book that has a very limited number of parts.
     
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  13. Threeneurons

    New Member

    Jul 12, 2016
    19
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    If you powered it all off of the same 5V, there was no power sequencing needed. The CD prefix simply meant it was made by RCA. RCA was bought by GE around the early 90's, then grouped with Harris, along with Intersil, Harris, and GE's semiconductor group, and spun off as the new Harris. Harris was eventually swallowed up by TI.

    The RCA CD4000 CMOS series came out in the 60s, and was dog slow. At 5V, it could barely clock at 3MHz. 74HC CMOS came out in around 1983. It could clock in excess of 25MHz.

    As for signal level, you could mix 4000 with 74HC with little regard, as long as they both used the same 5V supply. There was also 74HCT, which had input specs, that made it compatible with "real" TTL. For TTL, an input saw a logic-0, if the voltage was 0.8V or lower, and a logic-1 if it was 2.0V or higher. 74HCT aslo met these conditions. For 74HC, an input looked like a logic-0 if it was 30% of the supply (1.5V max for 5V), and 70% for a logic-1 (3.5V min for 5V). It was similar for 4000 series CMOS. A quick remedy, was to add a pull-up resistor to any TTL output going into a CMOS input.

    Old TTL used only NPN transistors on the output, in what was called a totem pole arrangement. It could sink a lot of current to GND, but could "source" only a fraction of it to a logic one. Typically, an output, could sink 16mA to a voltage of 0.4V max, but only source 0.8mA to 2.4V min, for logic-1 output. Very asymmetrical. CMOS on the other hand was very symmetrical.
     
  14. Threeneurons

    New Member

    Jul 12, 2016
    19
    10
    In the old days, there were lots of IC makers:

    RCA used the prefix of CD, for its digital logic chips, and CA for its analog chips.
    TI used SN, for both logic chips, and interface chips. Later TL for most of its analog chips.
    National Semiconductor used "DM" for digital monolithic. "MM" for MOS monolithic. "LM" for linear monolithic, and "LH" for linear hybrid. Probably a few more, that I forgot. The National MM74C series performed on the same level of RCA's 4000 series (slow as molasses), but had 7400 pinouts. Predates the 74HC series.
    The original Fairchild (not the one that regurgitated by National in the 90s) used uA (mu-A) for its linear chips, but also had a 9000 series logic family, which prefix I can't remember (uD ?).
    Signetics used NE and SE. Motorola used MC, and its MC14000 series was a 1-to-1 match of the RCA 4000 series.
     
  15. RichardO

    Well-Known Member

    May 4, 2013
    1,231
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    And many a purchasing agent accidentally bought the MC4040 instead of the MC14040 and received a TTL phase lock loop chip. :(
     
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