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I've read some of the data sheet for the TLC 5940 and it states the following about the BLANK input:

Blank all outputs. When BLANK = H, all OUTn outputs are forced OFF. GS counter is also reset. When BLANK = L, OUTn are controlled by grayscale PWM control.

Looking at this image: enter image description here

... from the Arduino playground about using the TLC chip with Arduino it shows a 10k pull-up resistor to reset the chips when the device is turned on.

I read about pull-up resistors so I get that when power is supplied the resistor allows BLANK to read a high input. What I don't get though is how the chip works after that. I don't see anything that sets BLANK to low.

How is the BLANK input getting set to LOW so the device can operate normally?

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The BLANK pin(s) on the TLC5940(s), in addition to being pulled high by the 10k resistor, are also tied to pin 10 of the Arduino (labeled "BLANK", the blue wire). This allows the Arduino firmware to drive the pin low when needed.

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  • \$\begingroup\$ Right ok so after the arduino boots it would set pin 10 to ground and that would make the BLANK input read LOW. Don't know how I missed that. Thank you. \$\endgroup\$
    – William
    Commented Oct 1, 2012 at 20:59

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