AN2707 Freescale Semiconductor / Motorola, AN2707 Datasheet - Page 6

• Manufacturer Part Number: AN2707
• Description: Software Drivers for Tango3 RF Transmitter and Romeo2 RF Receiver ICs
• Manufacturer: Freescale Semiconductor / Motorola

AN2707
Reducing Power
Consumption
6
Key
Generated by driver
Supplied by application/programmer
Rf signal from Tango3
Preamble
Preamble
Software Drivers for Tango3 RF Transmitter and Romeo2 RF Receiver ICs
ID
ID
Figure 3. Message Format Without Header Detection
it will pass all following data to the MCU via the SPI interface. See
the ID field is repeated, this will mean that ID bytes are also passed to the MCU.
This message format requires more CPU time to decode the received data,
since it must handle the ID field.
To reduce power consumption in the system, the drivers can utilize two
features of the Romeo2 device: the strobe oscillator; and the ability to repeat
the ID field. The Romeo2 datasheet includes a full description of the strobe
oscillator function.
The strobe oscillator function cycles Romeo2 between the very low power
SLEEP mode and a RUN mode, thereby reducing the total current
consumption. As mentioned previously, it is possible to repeat the Preamble
and ID sections of the message. If Tango3 transmits a sequence of short
Preamble + ID messages over a period longer than the strobe oscillator’s
SLEEP period, Romeo2 will detect at least one of these messages in RUN
mode. When this has been detected, Romeo2 will override its Strobe oscillator,
and will remain in RUN mode until it receives the remaining message fields.
Figure 4
ID detected
ID
ID
Freescale Semiconductor, Inc.
For More Information On This Product,
ID
shows the sequence.
………
Transfer without header byte
Go to: www.freescale.com
……
ID
ID
Length
Length
Data0
Data0
………
………
Data127
Data127
SPI output (Romeo2 to MCU)
Checksum EOM
Checksum
Figure
MOTOROLA
3. If