15.0 Low Power Modes
The LMX9838 supports different Low Power Modes to reduce
power in different operating situations. The modular structure
of the LMX9838 allows the firmware to power down unused
modules.
The Low power modes have influence on:
•
UART transport layer
– enabling or disabling the interface
•
Bluetooth Baseband activity
– firmware disables LLC and Radio if possible
15.1 POWER MODES
The following LMX9838 power modes, which depend on the
activity level of the UART transport layer and the radio activity
are defined:
The radio activity level mainly depends on application re-
quirements and is defined by standard bluetooth operations
like inquiry/page scanning or an active link.
A remote device establishing or disconnecting a link may also
indirectly change the radio activity level.
The UART transport layer by default is enabled on device
power up. In order to disable the transport layer the command
“Disable Transport Layer” is used. Thus only the Host side
command interface can disable the transport layer. Enabling
the transport layer is controlled by the HW Wakeup signalling.
This can be done from either the Host or the LMX9838. See
also “LMX9838 Software User’s Guide” for detailed informa-
tion on timing and implementation requirements.
TABLE 12. Power Mode Activity
Power
Mode
UART
Activity
Radio
Activity
Reference
Clock
PM0
OFF
OFF
none
PM1
ON
OFF
Main Clock
PM2
OFF
Scanning
Main Clock /
32.768 kHz
PM3
ON
Scanning
Main Clock
PM4
OFF
SPP Link
Main Clock
PM5
ON
SPP Link
Main Clock
30027921
FIGURE 6. Transition between different Hardware Power Modes
15.2 ENABLING AND DISABLING UART TRANSPORT
15.2.1 Hardware Wakeup Functionality
In certain usage scenarios the host is able to switch off the
transport layer of the LMX9838 in order to reduce power con-
sumption. Afterwards both devices, host and LMX9838 are
able to shut down their UART interfaces.
In order to save system connections the UART interface is
reconfigured to hardware wakeup functionality. For a detailed
timing and command functionality please see also the
“LMX9838 Software User’s Guide”. The interface between
host and LMX9838 is defined as described in Figure 7.
17
www.national.com
LMX9838
