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ADuCM360 Serial download mode criteria clarification

Question asked by rbaml on Feb 10, 2016
Latest reply on Feb 10, 2016 by rbaml

I plan to have a user button connected to the BM pin that serves as a named function in normal operation, and that if pressed and held during a power cycle (off to on) will initiate Serial Download Mode. I understand from the Serial Download protocol document, AN1160 that only a physical reset by asserting the reset pin will do, the power on reset will not work for this purpose.

 

So to solve this problem, I plan to include a circuit to hold the ADucM360 in reset for a short time after power on. So my question is, how long does the reset signal need to be asserted for to guarantee the bootloader has enough time to check the BM pin and take the proper action? The datasheet just says..

 

"When this pin [BM] is held low during and for a short time after any reset sequence, the part enters UART download mode."

 

Which is not very helpful. Short time ms? s?. I do not have any hardware to hand to test this experimentally. Any advice would be much appreciated,

 

Thanks

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