1.2.7
Battery
To continue operating when the mains power is cut, the M2MBoxPro embeds a 2000mAh lithium backup
battery. The modem can operate for several days without being recharged.
It is possible for the openAT software to detect whether it is powered by the battery or by the mains by sensing
GPIO12: if GPIO12 is high, the M2MBoxPro is powered by the mains. If GPIO12 is low, the device is powered
by the battery.
The battery has a given lifetime of more than 300 charge cycles. It is recommended that the customer appli-
cation software uses GPIO12 signal to count the number of charge cycles, so that it can estimate battery end
of life.
Note that the M2MBoxPro does not use the Q26’s integrated charging circuit, but an external one. The battery
voltage can be measured using the Q26’s ADC0 interface.
1.2.8
Digital inputs
The M2MBoxPro has 8 digital inputs. These are 0-24V rated and organized in two groups of four inputs, with
one common voltage reference for each group of four. All digital inputs are voltage transient protected, with
dissipation of 600W peak pulse power on 10/1000us waveform and 15A peak pulse current. For additional
protection, the digital inputs are opto-isolated and offer 3750Vrms isolation. The digital inputs are connected
to the Q26 CPU as follows:
Digital input
Q26 GPIO
0
10
1
8
2
6
3
5
4
7
5
13
6
11
7
9
For safety, the external power source that drives the inputs must be isolated from the M2MBoxPro power
source.
1.2.9
I²C port
The Q26 CPU I²C interface is available on the casing for connecting to external pieces of hardware, on Grey
screw terminal connector.
The interface is four pins, including the two SCL and SDA signals, a ground pin and a 2.8V voltage output. The
2.8V output is to be used as a voltage reference and can provide up to 100mA to power small I²C peripherals.
There are no pull-up resistors inside the devices. If needed, these will have to be added externally, but can be
connected to the 2.8V reference voltage. If not using this voltage reference, note that the absolute maximum
voltage that can be applied on the I²C signals is 3.1V.
The pin assignment is as follows:
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