D latch 47LS374 Problem

Discussion in 'General Electronics Chat' started by syee10, Mar 28, 2011.

  1. syee10

    Thread Starter Member

    Mar 26, 2010
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  2. SgtWookie

    Expert

    Jul 17, 2007
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  3. syee10

    Thread Starter Member

    Mar 26, 2010
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    Sorry i dun get you. My condition is like this. I connect a decade counter 74ls90 with the latch 74ls374 and a bcd to 7 segment decoder 74ls47 and finally the 7 segment display. When i power up the circuit, the circuits start to count and 7 segment display shows the count. When i turn off the circuit, the circuits stop. And now when i turn on the circuit again, the 7 segment display count from a weird value and it does not count from 0.
    How am i going to make it start from counting 0 every time i power up the circuit? Is it because of the latch memory?
     
  4. SgtWookie

    Expert

    Jul 17, 2007
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    It sounds to me like your 74LS90 decade counter is not being initialized properly on start-up.

    Both SET inputs should be held low, and the RESET inputs set momentarily high to zero the counter.
     
  5. syee10

    Thread Starter Member

    Mar 26, 2010
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    Unfortunately i cant find any reset pin at the 74LS90 decade counter. So how am i going to reset the counter?
     
  6. t06afre

    AAC Fanatic!

    May 11, 2009
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    Look in the datasheet. Read about the MR1, MR2, MS1 and the MS2 pin (2,3 6,7). It may also count strange if the CP1 pin is not corretly connected
     
  7. syee10

    Thread Starter Member

    Mar 26, 2010
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    I think i found out the solution.. Isit the solution as below?

    Pins 2 and 3 are master reset and will clear the 74LS90 to zero. High on pins 2 and 3 with pins 6 and 7 low will clear to zero.

    Pins 6 and 7 are master set and will set the 74LS90 to nine. High on pins 6 and 7 with pins 2 and 3 low will set to nine.
     
  8. t06afre

    AAC Fanatic!

    May 11, 2009
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    Yes that it correct. Also remember to not float input pins then working with digital logic. A floating TTL input pin (not connected) will as thumb rule see logical one. But never depend on that in circuit design.
     
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