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[SOLVED] Shift Register Issues

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venkates2218

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Hai,
Already discussed regarding this in below topic.


Please refer the image.
For Example:When power failure occurred and power resumed means,some times outputs are switched ON with previous state without enabling the OE pin.How to avoid this issue.?
 

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venkates2218 said:
some times outputs are switched ON with previous state without enabling the OE pin.
Click to expand...
This surely doesn't happen. Outputs are tri-stated as long OE is disabled (High). Output registers have however undefined state before they are loaded from shift register.
 

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Hi,

I agree with FvM.

Independent of register state: as long as OE is disabled the output is HIGH IMPEDANCE wich is neither defined as LOW nor HIGH ...
If you want defined LOW ro HIGH (when OE is disabled) you need to add pull-up or pull-down resistors.

Klaus
 

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Removed the IC from board and tired with shift register alone.During that time there is no output is switched ON.But when IC is used means,the outputs going to high at time required to MCU configure.When the 1st sequence is started after port configure of MCU,there is no error in shift register.
 

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Hi,

Nobody said there is an error in shift register.
We talk about undefined states. It seems you ignored this.

For further discussion: show your schematic.

Klaus
 

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KlausST said:
Hi,

Nobody said there is an error in shift register.
We talk about undefined states. It seems you ignored this.

For further discussion: show your schematic.

Klaus
Click to expand...
Sorry picked an wrong word.When MCU is removed the outputs of shift registers in low state.If MCU is connected with shift register means for the outputs are going to high state at initial time only.After running the port configure sequence outputs in shift register in low state
 

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Inappropriate initialisation. Correct state must be clocked into the output register before activating output enable.
 

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