LMX9820SB/NOPB National Semiconductor, LMX9820SB/NOPB Datasheet - Page 23

• Manufacturer Part Number: LMX9820SB/NOPB
• Manufacturer: National Semiconductor

Specifications of LMX9820SB/NOPB

• Lead Free Status / Rohs Status: Compliant

Revision 1.0
11.0 Low Power Modes
The LMX9820 supports different Low Power Modes to
reduce power in different operating situations. The modular
structure of the LMX9820 allows the firmware to power
down unused modules.
The Low power modes have influence on:
• UART transport layer
• Bluetooth Baseband activity
11.1 POWER MODES
The following LMX9820 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
requirements and is defined by standard bluetooth opera-
tions 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 com-
mand “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
and the LMX9820. See also “LMX9820 Software Users
Guide” for detailed information on timing and implementa-
tion requirements.
11.2 ENABLING AND DISABLING UART
TRANSPORT
11.2.1 Hardware Wake up functionality
In certain usage scenarios the host is able to switch off the
transport layer of the LMX9820 in order to reduce power
consumption. Afterwards both devices, host and LMX9820
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 “LMX9820 Software Users Guide”.
The interface between host and LMX9820 is defined as
described in Figure 16.
Power
Mode
PM0
PM1
PM2
PM3
PM4
PM5
– enabling or disabling the interface
– firmware disables LLC and Radio if possible
Table 26. Power Mode activity
UART activity
OFF
ON
OFF
ON
OFF
ON
Radio activity
OFF
OFF
Scanning
Scanning
SPP Link
SPP Link
23
11.2.2 Disabling the UART transport layer
The Host can disable the UART transport layer by sending
the “Disable Transport Layer” Command. The LMX9820
will empty its buffers, send the confirmation event and dis-
able its UART interface. Afterwards the UART interface will
be reconfigured to wake up on a falling edge of the CTS
pin.
11.2.3 LMX9820 enabling the UART interface
As the Transport Layer can be disabled in any situation the
LMX9820 must first make sure the transport layer is
enabled before sending data to the host. Possible scenar-
ios can be incoming data or incoming link indicators. If the
UART is not enabled the LMX9820 assumes that the Host
is sleeping and waking it up by activating RTS and setting
HOST_WU to 1. To be able to react on that Wake up, the
host has to monitor the CTS pin.
As soon as the host activates its RTS pin, the LMX9820 will
first send a confirmation event and then start to transmit
the events.
11.2.4 Enabling the UART transport layer from the host
If the host needs to send data or commands to the
LMX9820 while the UART Transport Layer is disabled it
must first assume that the LMX9820 is sleeping and wake
it up using its RTS signal.
When the LMX9820 detects the Wake-Up signal it acti-
vates the UART HW and acknowledges the Wake-Up sig-
nal by settings its RTS and HOST_WU signal. Additionally
the Wake up will be confirmed by a confirmation event.
When the Host has received this “Transport Layer
Enabled” event, the LMX9820 is ready to receive com-
mands.
.
LMX9820
Figure 16. UART NULL modem connection
Host_WU
RTS#
CTS#
RX
TX
(optional)
RTS#
CTS#
TX
RX
GPIO
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Host