Integration Manual
ANNA-B4 series - System integration manual
UBX-21000517 - R03 Contents Page 16 of 76
C1-Public
Depending on the software settings, the internal oscillator itself adds ~400 nA to the current
consumption and the calibration of the oscillator adds another ~1 µA. The standby current of
ANNA-B4 then increases from 2.2 µA to 3.6 µA, which is an increase of ~60%. For information about
the possible settings using open CPU software, see also the application note RC oscillator
configuration for nRF5 open CPU modules [8].
☞ Low Frequency Clock settings are fixed for use with u-connectXpress software.
For applications where only the active mode is used, and the module never or rarely is in standby, the
increase of current is negligible.
If the application is expected to be in standby for longer periods of time and it is powered from a
battery, it might be worth adding an external crystal.
Table 9 shows the average current consumption for a beacon advertising at different intervals, when
using an external crystal oscillator versus when using the internal oscillator. The use case shown here
is based on an advertisement event (4.7 ms) that is broadcast with +4 dBm output power, 31 bytes,
and 3.3 V payload.
Table 9: Average current consumption with/without external low power crystal (theoretical calculations)
2.6 Serial interfaces
The pin mapping of the supported interfaces is dependent on whether ANNA-B4 is used with
u-connectXpress software or an open CPU based application. See also the ANNA-B402 [5] and
ANNA-B412 [6] data sheets.
Universal asynchronous serial interface (UART)
ANNA-B4 series modules provide 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 DTR are used to set and indicate system modes
The UART can be used as a 4-wire UART with hardware flow control or 2-wire UART with only TXD
and RXD. In 2-wire mode, CTS should be connected to GND on the ANNA-B4 module.
The bootloader delivered with the product, either u-connectXpress bootloader or the Nordic DFU
bootloader for open CPU modules, can be used to upgrade the software over the UART interface.
See also Flashing over the UART interface and Flashing ANNA-B412 u-connectXpress software.
The u-connectXpress software adds the DSR and DTR pins to the UART interface. These pins are not
used as originally intended but are used instead to control the state of the ANNA-B412 module.
Depending on the configuration of u-connectXpress, the DSR can be used to:
• Enter command mode
• Disconnect and/or toggle connectable status
• Enable/disable the rest of the UART interface
• Enter/wake up from the sleep mode
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 %