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Connect ME and ME 9210 reset pin recommendations

Hardware reference manual http://ftp1.digi.com/support/documentation/90001247_C.pdf statement about RESET:

Pulling pin 8 low with an open drain driver will force the module into a hard reset state. The module will remain in the reset state as long and pin 8 is held low and will leave this reset state ~250mS after pin 8 goes high. Do not actively drive pin 8 high and do not allow the rise time of the pin 14 to be longer than 100uS. When used with the development board, this pin is wired to reset button SW4, which means it acts as a hard reset button.

The Digi Connect Wi-ME 9210 module supports a hardware reset via pin 8 of the 14-pin header. The unit is forced into a hard reset when pulling the pin to ground, or less than 0.8v, for one microsecond. When plugged into a development board, this pin is wired to the push button at SW4. As a result, this switch acts as a hard reset button.


Additional information:
Make sure the reset signal is pulled up with a resistor and achieves the correct logic level voltages and NEVER back drives (actively drive high) ANY signals into the Digi Connect ME 9210 (or ME) before and during the ME's 3.3V power up. Driving back power through the ME’s signal or reset lines before power up, can cause the ME's processor to either partially power up and behave very unpredictable ways or worse, can cause a CMOS latch up ---- both will persist as long as the ME is powered and MAY cease with a power cycle. If the processor enters some peculiar operational state due to back driving the ME's signals during power up, there is NO guarantee that anything, including reset, will work.

If you want to avoid back driving power into the ME before it powers up, make sure your external CPU powers up later, or all connected signals are in a tri-state (configured as input for your external CPU as power up default). It this is not possible add tri-stated buffers between the driven Connect ME (9210) signals and the active external CPU driver. The ME’s signals can be driven as soon as the ME’s power is present and stable. Pulling signal high with a modest value pull up resistor is ok, because it doesn’t drive much current into the un-powered ME signal pin.
Last updated: Aug 08, 2017

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