Ensuring a TLC5947 device is disabled on power up.

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Hi Guys,

 

I have a string of TLC5947's attached to an ATmega328p.  There is a pin(Blank Pin) on the TLC5947 that disables output if it is high.  Currently the first bit of code sets PD7 high in addition 10 a 10K resistor.  

 

I want to have the TLC5947 blank pin high as the 328p is starting as the current draw with outputs on could stall the 328P before it executes the code.

 

Obviously the solution would be to have the TLC5947 Blank pin feed 5v from the board power, but I'm unsure as to the best way of configuring the Pin on the 328P such I can then bring the TLC5947 blank pin low.  

 

I'm sure there's an obvious solution but it's escaping me at the moment.

 

Any help would be appreciated.

 

regards

 

This topic has a solution.

 

 

Last Edited: Tue. Sep 10, 2019 - 08:32 PM
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Please provide:
Schematic
Link to what ever a TLC5947 is.
Or did you intend for us to look it all up?
Generally, if a pin needs to be high while an AVR is in reset, an external pull-up resister is used.
Jim
Ok, I pulled a DS, you need a 10k pull-up on that line so the AVR can init the device before the outputs
Are enabled by putting “blank” line low!

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Last Edited: Tue. Sep 10, 2019 - 07:52 PM
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sorry, my bad, data sheet is here 

 

Generally, if a pin needs to be high while an AVR is in reset, an external pull-up resister is used.

 

Thanks, but yes I understand that.  My question is, how do I pull it down on command?

 

regards

 

 

 

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nikm wrote:

sorry, my bad, data sheet is here 

 

Generally, if a pin needs to be high while an AVR is in reset, an external pull-up resister is used.

 

Thanks, but yes I understand that.  My question is, how do I pull it down on command?

 

regards

 


Connect it to a port pin, once the chip is initiated, make your port pin an output and set it low.

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Ahh,

 

Just to get this straight that's all I need to do with the setup below?

 

regards

 

5v -> 10k resistor ----- > Blank pin on TLC
                             |
                             v
                           PB7 on 328P (as output)

 

So setting PB7 low will sink voltage?

 

 

 

This reply has been marked as the solution. 
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nikm wrote:

Ahh,

 

Just to get this straight that's all I need to do with the setup below?

 

regards

 

5v -> 10k resistor ----- > Blank pin on TLC
                             |
                             v
                           PB7 on 328P (as output)

 

So setting PB7 low will sink voltage?

 

Yes!

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Last Edited: Tue. Sep 10, 2019 - 08:08 PM
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Sweet, thank you.  

 

That said I'm having a hard time understanding why setting an output pin to low would sink the line to 0v unless the effect is to ground it. 

 

regards

 

 

 

Last Edited: Tue. Sep 10, 2019 - 08:12 PM
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nikm wrote:
I'm having a hard time understanding why setting an output pin to low would sink the line to 0v

Why is that hard to understand?

 

"Setting a pin low" means, literally, "pulling it to 0V".

 

"Set pin low" and "set pin to 0V" and "ground the pin" are pretty much synonymous.

 

to put it another way: "low" = 0V = ground (conventionally).

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Last Edited: Tue. Sep 10, 2019 - 08:29 PM
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Now I understand.  Thanks for the explanation

 

regards

 

 

 

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Top Tips:

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  2. "Garbage" characters on a serial terminal are (almost?) invariably due to wrong baud rate - see: https://learn.sparkfun.com/tutorials/serial-communication
  3. Wrong baud rate is usually due to not running at the speed you thought; check by blinking a LED to see if you get the speed you expected
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