User's Manual

HE920 Hardware User Guide
1vv0301014 Rev.9 – 2014-01-23
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Reserved. Page 26 of 84
NOTE:
To check if the HE920 has powered on, the hardware line PWRMON must be monitored.
When PWRMON goes high, the module has powered on.
NOTE:
Do not use any pull up resistor on the ON_OFF* line, it is internally pulled up. Using pull up
resistor may bring to latch up problems on the HE920 power regulator and improper power
on/off of the module. The line ON_OFF* must be connected only in open collector
configuration.
NOTE:
In this document all the lines are inverted. Active low signals are labeled with a name that
ends with "#", "*" or with a bar over the name.
NOTE:
In order to avoid a back powering effect it is recommended to avoid having any HIGH logic
level signal applied to the digital pins of the module when is powered OFF or during an
ON/OFF transition.
For example:
1- Let us assume you need to drive the ON_OFF* pad with a totem pole output of a +1.8/5
V microcontroller (uP_OUT1):