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CD74HC4514: Latch Enable and Output Enable

Sivaraman Radhakrishnan
Prodigy 130 points

Part Number: CD74HC4514

Hi TI,

i want to understand the Latch enable function based on naming LE\. LE\ is Active low signal enable. But in Decode Truth table derived with LE\ = 1. what shall be Decoder output when LE\ is logic low?

I am planning to include Pull up or Pull down for all the signal lines based on the function. Shall i add Pull up or Pull down for Latch enable line? (based on assumption - Pull down, Correct me if i am wrong)

I have added pull up for Output Enable line.

Also please confirm the below sequence.

Step 0. Default mode: E\ = 1; LE\ disabled (0) ; DATA (A,B,C,D) = X(dont care);

Step 1. Setting DATA(A,B,C,D) = Any Value Example 0000;

Step 2. Setting E\ to Logic Low (0) from Logic High(1);

Step 3. LE\ is enabled for 20ms pulse (Logic high).

Step 4. After the selection, Decoder is disable by making E\ as logic high to disable the Decoder output.

Please provide your thoughts on this.

Thanks,

Siva

  • 0
    Guru 325400 points

    When LE is high, the decoder uses the current state of the four Ax inputs.
    When LE is low, the decoder uses the state that the four Ax inputs had when LE was high previously.

    Whether to use a pull-up or a pull-down depends on what value you want to have when the signal is not driven by another device.

    You should enable E after LE to ensure that only the new value is visible at the outputs.