ANNA-B112 - System integration manual
UBX-18009821 - R09
System description
Page 14 of 66
C1-Public
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2-32: Check the temperature and calibrate only if it has changed; however, calibration will take
place every X count of the
calibration timer interval even if there is no change in the temperature.
Calibrating the unit more often will increase the current consumption.
⚠
When using internal oscillator as source the user must make sure that the settings calibrate the
internal oscillator at least once every 8 seconds to /-250ppm clock stability. It is
recommended to keep the default values as stated in Table 6.
1.6.5
Selecting clock source
As described above, the selection of clock source is a tradeoff between BOM count and current
consumption. The increase in current consumption when using the internal oscillator will depend on
both the software settings as well as the surrounding environment.
The internal oscillator itself will add about 400 nA and the calibration will add about 1 µA, depending
on the above-mentioned settings. The standby current of ANNA-B112 will then increase from 2.2 µA
to 3.6 µA, an increase of about 60%.
For the active use cases when the module is not in standby the increase of current is negligible. So if
the application will be in standby for longer periods of time then an external crystal might be worth
adding.
Table 7 shows the average current consumption for a beacon advertising at different intervals, both
with external crystal oscillator as well as internal oscillator. The use case is an advertisement event
(4.7 ms), +4 dBm output power and 31 bytes payload at 3.3 V.
Debug – serial wire debug (SWD)
The primary interface for debug is the SWD interface. The SWD interface can also be used for
software upgrade.
The two pins,
SWDIO
and
SWDCLK
, should be made accessible on header or test points.
Serial interfaces
⚠
The available interfaces and pin mapping can differ depending on if ANNA-B112 is used with the
u-connectXpress software or an open CPU based application. For detailed pin information see the
ANNA-B112 data sheet [2].
1.8.1
Universal asynchronous serial interface (UART)
The ANNA-B112 module provides a Universal Asynchronous Serial Interface (UART) for data
communication.
The following UART signals are available:
•
Data lines (
RXD
as input,
TXD
as output)
•
Hardware flow control lines (
CTS
as input,
RTS
as output)
•
DSR
and
DTS
are used to set and indicate system modes
Advertise interval
External crystal oscillator Internal oscillator
Increase in current
1 s
18 µA
19.5 µA
8 %
10 s
3.8 µA
5.2 µA
37 %
60 s
2.4 µA
3.9 µA
63 %
Table 7: Average current consumption (theoretical calculations)
