SCHA005B January   2015  – December 2022 74AC11074 , 74AC16373 , 74AC16374 , 74ACT11074 , 74ACT11373 , 74ACT11374 , 74ACT16373 , 74ACT16374 , 74ACT16823 , 74ACT16841 , CD4006B-MIL , CD4013B , CD4013B-MIL , CD4014B , CD4014B-MIL , CD4015B , CD4015B-MIL , CD40174B , CD40174B-MIL , CD40175B , CD40175B-MIL , CD40194B , CD4021B , CD4021B-MIL , CD4021B-Q1 , CD4027B , CD4027B-MIL , CD4031B , CD4031B-MIL , CD4034B , CD4034B-MIL , CD4035B , CD4035B-MIL , CD4042B , CD4042B-MIL , CD4043B , CD4043B-MIL , CD4044B , CD4044B-MIL , CD4076B , CD4076B-MIL , CD4094B , CD4094B-MIL , CD4099B , CD4099B-MIL , CD4508B , CD4508B-MIL , CD4517B , CD4517B-MIL , CD4724B , CD4724B-MIL , CD54AC109 , CD54AC112 , CD54AC164 , CD54AC273 , CD54AC299 , CD54AC373 , CD54AC374 , CD54AC573 , CD54AC574 , CD54AC74 , CD54ACT109 , CD54ACT112 , CD54ACT164 , CD54ACT174 , CD54ACT273 , CD54ACT299 , CD54ACT373 , CD54ACT374 , CD54ACT573 , CD54ACT574 , CD54ACT74 , CD54HC107 , CD54HC109 , CD54HC112 , CD54HC164 , CD54HC165 , CD54HC166 , CD54HC173 , CD54HC174 , CD54HC175 , CD54HC194 , CD54HC259 , CD54HC273 , CD54HC299 , CD54HC373 , CD54HC374 , CD54HC377 , CD54HC4015 , CD54HC4094 , CD54HC533 , CD54HC534 , CD54HC563 , CD54HC564 , CD54HC573 , CD54HC574 , CD54HC597 , CD54HC73 , CD54HC74 , CD54HC75 , CD54HCT109 , CD54HCT112 , CD54HCT164 , CD54HCT165 , CD54HCT166 , CD54HCT173 , CD54HCT174 , CD54HCT175 , CD54HCT259 , CD54HCT273 , CD54HCT299 , CD54HCT373 , CD54HCT374 , CD54HCT377 , CD54HCT533 , CD54HCT534 , CD54HCT564 , CD54HCT573 , CD54HCT574 , CD54HCT74 , CD54HCT75 , CD74AC109 , CD74AC112 , CD74AC164 , CD74AC174 , CD74AC175 , CD74AC273 , CD74AC299 , CD74AC323 , CD74AC373 , CD74AC374 , CD74AC534 , CD74AC573 , CD74AC574 , CD74AC74 , CD74ACT109 , CD74ACT112 , CD74ACT164 , CD74ACT174 , CD74ACT175 , CD74ACT273 , CD74ACT299 , CD74ACT373 , CD74ACT374 , CD74ACT573 , CD74ACT574 , CD74ACT74 , CD74ACT74-Q1 , CD74FCT273 , CD74FCT374 , CD74FCT843A , CD74HC107 , CD74HC109 , CD74HC112 , CD74HC164 , CD74HC165 , CD74HC166 , CD74HC173 , CD74HC174 , CD74HC175 , CD74HC194 , CD74HC195 , CD74HC259 , CD74HC273 , CD74HC299 , CD74HC373 , CD74HC374 , CD74HC377 , CD74HC4015 , CD74HC4094 , CD74HC533 , CD74HC534 , CD74HC563 , CD74HC564 , CD74HC573 , CD74HC574 , CD74HC595 , CD74HC597 , CD74HC670 , CD74HC73 , CD74HC74 , CD74HC75 , CD74HCT107 , CD74HCT109 , CD74HCT112 , CD74HCT164 , CD74HCT165 , CD74HCT166 , CD74HCT173 , CD74HCT174 , CD74HCT175 , CD74HCT194 , CD74HCT259 , CD74HCT273 , CD74HCT299 , CD74HCT373 , CD74HCT374 , CD74HCT377 , CD74HCT4094 , CD74HCT533 , CD74HCT534 , CD74HCT563 , CD74HCT564 , CD74HCT573 , CD74HCT574 , CD74HCT574-EP , CD74HCT574-Q1 , CD74HCT597 , CD74HCT670 , CD74HCT73 , CD74HCT74 , CD74HCT75 , CY54FCT273T , CY54FCT373T , CY54FCT374T , CY54FCT377T , CY54FCT573T , CY54FCT574T , CY54FCT841T , CY74FCT162374T , CY74FCT16374T , CY74FCT2373T , CY74FCT2573T , CY74FCT2574T , CY74FCT273T , CY74FCT373T , CY74FCT374T , CY74FCT573T , CY74FCT574T , SN54107 , SN54166 , SN54173 , SN5472 , SN5476 , SN54ABT16373A , SN54ABT16374A , SN54ABT273 , SN54ABT373 , SN54ABT374 , SN54ABT377 , SN54ABT533 , SN54ABT534 , SN54ABT573 , SN54ABT574 , SN54ABT821 , SN54ABT823 , SN54ABT841 , SN54ABT843 , SN54AC373 , SN54AC373-SP , SN54AC374 , SN54AC574 , SN54AC74 , SN54AC74-SP , SN54ACT16373 , SN54ACT373 , SN54ACT373-SP , SN54ACT374 , SN54ACT374-SP , SN54ACT573 , SN54ACT74 , SN54AHC273 , SN54AHC373 , SN54AHC374 , SN54AHC573 , SN54AHC574 , SN54AHC74 , SN54AHCT373 , SN54AHCT374 , SN54AHCT573 , SN54AHCT574 , SN54AHCT74 , SN54ALS109A , SN54ALS112A , SN54ALS174 , SN54ALS175 , SN54ALS259 , SN54ALS273 , SN54ALS29821 , SN54ALS299 , SN54ALS323 , SN54ALS373A , SN54ALS374A , SN54ALS563B , SN54ALS564B , SN54ALS573C , SN54ALS574B , SN54ALS576B , SN54ALS580B , SN54ALS74A , SN54ALS873B , SN54ALS874B , SN54ALS996 , SN54AS174 , SN54AS175B , SN54AS374 , SN54AS573A , SN54AS574 , SN54AS74A , SN54AS821A , SN54AS823A , SN54AS825A , SN54BCT373 , SN54BCT374 , SN54BCT574 , SN54BCT8374A , SN54F109 , SN54F373 , SN54F374 , SN54F74 , SN54HC109 , SN54HC109-SP , SN54HC112 , SN54HC164 , SN54HC164-SP , SN54HC165 , SN54HC166 , SN54HC166-SP , SN54HC174 , SN54HC175 , SN54HC195 , SN54HC259 , SN54HC273 , SN54HC273-DIE , SN54HC273-SP , SN54HC373 , SN54HC373-DIE , SN54HC373-SP , SN54HC374 , SN54HC374-SP , SN54HC377 , SN54HC573A , SN54HC573A-SP , SN54HC574 , SN54HC595 , SN54HC595-SP , SN54HC74 , SN54HC74-SP , SN54HCT373 , SN54HCT373-SP , SN54HCT374 , SN54HCT74 , SN54LS109A , SN54LS112A , SN54LS164 , SN54LS164-SP , SN54LS165A , SN54LS165A-SP , SN54LS166A , SN54LS173A , SN54LS174 , SN54LS175 , SN54LS194A , SN54LS195A , SN54LS273 , SN54LS273-SP , SN54LS279A , SN54LS299 , SN54LS323 , SN54LS373 , SN54LS373-SP , SN54LS374 , SN54LS375 , SN54LS377 , SN54LS378 , SN54LS379 , SN54LS595 , SN54LS597 , SN54LS670 , SN54LS673 , SN54LS674 , SN54LS73A , SN54LS74A , SN54LS74A-SP , SN54LS75 , SN54LS76A , SN54LS91 , SN54LVC373A , SN54LVC374A , SN54LVC573A , SN54LVC574A , SN54LVC74A , SN54LVC74A-SP , SN54LVTH162373-SP , SN54LVTH162374-SP , SN54LVTH16373 , SN54LVTH373 , SN54LVTH374 , SN54LVTH573 , SN54LVTH574 , SN54LVTH574-SP , SN54S112 , SN54S174 , SN54S175 , SN54S194 , SN54S373 , SN54S374 , SN54S74 , SN74ABT162823A , SN74ABT162841 , SN74ABT16373A , SN74ABT16373A-EP , SN74ABT16374A , SN74ABT16821 , SN74ABT16823 , SN74ABT16841 , SN74ABT16843 , SN74ABT273 , SN74ABT373 , SN74ABT374A , SN74ABT377A , SN74ABT533A , SN74ABT534A , SN74ABT573A , SN74ABT574A , SN74ABT821A , SN74ABT823 , SN74ABT841A , SN74ABT843 , SN74ABTH162260 , SN74ABTH16260 , SN74ABTH16823 , SN74AC373 , SN74AC373-EP , SN74AC374 , SN74AC533 , SN74AC534 , SN74AC563 , SN74AC564 , SN74AC573 , SN74AC574 , SN74AC74 , SN74AC74-EP , SN74ACT16373-EP , SN74ACT16374-EP , SN74ACT373 , SN74ACT373-EP , SN74ACT374 , SN74ACT533 , SN74ACT534 , SN74ACT563 , SN74ACT564 , SN74ACT573 , SN74ACT574 , SN74ACT74 , SN74ACT74-EP , SN74AHC16373 , SN74AHC16374 , SN74AHC174 , SN74AHC273 , SN74AHC373 , SN74AHC374 , SN74AHC573 , SN74AHC574 , SN74AHC594 , SN74AHC595 , SN74AHC595-Q1 , SN74AHC74 , SN74AHC74-EP , SN74AHC74Q-Q1 , SN74AHCT16373 , SN74AHCT16374 , SN74AHCT174 , SN74AHCT273 , SN74AHCT373 , SN74AHCT374 , SN74AHCT573 , SN74AHCT574 , SN74AHCT594 , SN74AHCT595 , SN74AHCT74 , SN74AHCT74-EP , SN74AHCT74Q-Q1 , SN74ALS109A , SN74ALS112A , SN74ALS164A , SN74ALS165 , SN74ALS166 , SN74ALS174 , SN74ALS175 , SN74ALS259 , SN74ALS273 , SN74ALS29821 , SN74ALS299 , SN74ALS323 , SN74ALS373A , SN74ALS374A , SN74ALS533A , SN74ALS534A , SN74ALS563B , SN74ALS564B , SN74ALS573C , SN74ALS574B , SN74ALS575A , SN74ALS576B , SN74ALS577A , SN74ALS580B , SN74ALS666 , SN74ALS667 , SN74ALS74A , SN74ALS841 , SN74ALS843 , SN74ALS873B , SN74ALS874B , SN74ALS990 , SN74ALS992 , SN74ALS996 , SN74ALVCH162260 , SN74ALVCH162373 , SN74ALVCH162374 , SN74ALVCH16260 , SN74ALVCH162721 , SN74ALVCH162841 , SN74ALVCH16373 , SN74ALVCH16374 , SN74ALVCH16721 , SN74ALVCH16820 , SN74ALVCH16821 , SN74ALVCH16823 , SN74ALVCH16841 , SN74ALVCH373 , SN74ALVCH374 , SN74ALVTH16373 , SN74ALVTH16374 , SN74ALVTH16821 , SN74AS109A , SN74AS174 , SN74AS175B , SN74AS194 , SN74AS373 , SN74AS374 , SN74AS573A , SN74AS574 , SN74AS576 , SN74AS74A , SN74AS874 , SN74AUC16373 , SN74AUC16374 , SN74AUC1G74 , SN74AUC1G79 , SN74AUC1G80 , SN74AUC2G79 , SN74AUC2G80 , SN74AUC74 , SN74AUCH16374 , SN74AUP1G74 , SN74AUP1G79 , SN74AUP1G80 , SN74AUP2G79 , SN74AUP2G80 , SN74AVC16373 , SN74AVC16374 , SN74AVC16722 , SN74BCT374 , SN74BCT573 , SN74BCT574 , SN74F109 , SN74F112 , SN74F174A , SN74F175 , SN74F299 , SN74F373 , SN74F374 , SN74F377A , SN74F573 , SN74F574 , SN74F74 , SN74HC109 , SN74HC112 , SN74HC164 , SN74HC165 , SN74HC165-EP , SN74HC165-Q1 , SN74HC166 , SN74HC166A-EP , SN74HC166A-Q1 , SN74HC174 , SN74HC175 , SN74HC259 , SN74HC273 , SN74HC273-Q1 , SN74HC373 , SN74HC374 , SN74HC377 , SN74HC563 , SN74HC573A , SN74HC573A-Q1 , SN74HC574 , SN74HC594 , SN74HC595 , SN74HC595-EP , SN74HC74 , SN74HC74-EP , SN74HC74-Q1 , SN74HCT273 , SN74HCT373 , SN74HCT374 , SN74HCT377 , SN74HCT573 , SN74HCT574 , SN74HCT74 , SN74LS107A , SN74LS109A , SN74LS112A , SN74LS164 , SN74LS165A , SN74LS166A , SN74LS173A , SN74LS174 , SN74LS175 , SN74LS194A , SN74LS259B , SN74LS273 , SN74LS279A , SN74LS299 , SN74LS373 , SN74LS374 , SN74LS375 , SN74LS377 , SN74LS378 , SN74LS594 , SN74LS595 , SN74LS597 , SN74LS598 , SN74LS670 , SN74LS673 , SN74LS674 , SN74LS73A , SN74LS74A , SN74LS75 , SN74LV164A , SN74LV165A , SN74LV165A-EP , SN74LV165A-Q1 , SN74LV166A , SN74LV174A , SN74LV175A , SN74LV273A , SN74LV373A , SN74LV373A-Q1 , SN74LV373AT , SN74LV374A , SN74LV374A-EP , SN74LV374A-Q1 , SN74LV374AT , SN74LV573A , SN74LV573AT , SN74LV574A , SN74LV594A , SN74LV595A , SN74LV595A-EP , SN74LV595A-Q1 , SN74LV74A , SN74LV74A-EP , SN74LV74A-Q1 , SN74LV8153 , SN74LV8153-Q1 , SN74LVC112A , SN74LVC16373 , SN74LVC16373A , SN74LVC16373A-EP , SN74LVC16374 , SN74LVC16374A , SN74LVC1G175 , SN74LVC1G175-EP , SN74LVC1G373 , SN74LVC1G374 , SN74LVC1G374-Q1 , SN74LVC1G74 , SN74LVC1G79 , SN74LVC1G79-EP , SN74LVC1G80 , SN74LVC2G74 , SN74LVC2G74-EP , SN74LVC2G74-Q1 , SN74LVC2G79 , SN74LVC2G80 , SN74LVC373A , SN74LVC373A-EP , SN74LVC374A , SN74LVC374A-EP , SN74LVC374A-Q1 , SN74LVC573A , SN74LVC573A-EP , SN74LVC573A-Q1 , SN74LVC574A , SN74LVC574A-EP , SN74LVC574A-Q1 , SN74LVC74A , SN74LVC74A-EP , SN74LVC74A-Q1 , SN74LVC821A , SN74LVC823A , SN74LVC841A , SN74LVCH16373A , SN74LVCH16374A , SN74LVCH32373A , SN74LVTH162373 , SN74LVTH162373-EP , SN74LVTH162374 , SN74LVTH16373 , SN74LVTH16373-EP , SN74LVTH16374 , SN74LVTH16374-EP , SN74LVTH273 , SN74LVTH273-EP , SN74LVTH373 , SN74LVTH373-EP , SN74LVTH374 , SN74LVTH374-EP , SN74LVTH573 , SN74LVTH573-EP , SN74LVTH574 , SN74LVTH574-EP , SN74S112A , SN74S175 , SN74S374 , SN74S74

PRODMIX  

  1.   Power-Up Behavior of Clocked Devices
  2. 1Unknown States at Power-Up
  3. 2Solutions to Unknown States at Power-Up
    1. 2.1 Use a Device with Clear or Preset Pins
    2. 2.2 Delay the Clock Edge with an RC Circuit and Schmitt Trigger Buffer
    3. 2.3 Wait Until VCC Has Ramped
  4. 3Trademarks
  5. 4Revision History

2.1 Use a Device with Clear or Preset Pins

Some devices come with input pins designed to ensure a specific state upon power up. For example, an alternative to the CD74HC4094 is the CD74HC299, which contains a Master Reset ( MR) pin, which sets all outputs low when the pin is pulled low. The outputs will be set low regardless of the state of the clock pulse (see the truth table in the datasheet). Other devices, such as the SN74HC74, have clear ( CLR or CLR) and preset ( PRE or PRE) pins. When active, the clear pins set the outputs low, and the preset pins set the outputs high, regardless of CLK. The polarities of the clear and preset pins vary among different parts, and it is typically not recommended to activate both of them at the same time (nonstable configuration). The truth table in the device datasheet specifies which configurations are not recommended.

The example in Figure 2-1 shows a configuration where the user wants an initial high output at Q. According to the truth table, this requires a high CLR and a low PRE. Use pullup resistors to connect the inputs to the appropriate levels. After power-up, the truth table says that PRE must then be pulled high to allow Data and CLK to control the output. The pullup resistor must be sized such that the device driving PRE can overdrive the pullup resistor while keeping PRE above its VIH level.

GUID-8C05F6EE-8C8E-4198-A7B8-FD6647CE46EF-low.gifFigure 2-1 SN74HC74 Partial Schematic for High Power-Up Output at Q