Datasheet

486
SAM9M10 [DATASHEET]
6355F–ATARM–12-Mar-13
Figure 31-17. Manchester Encoded Characters RF Transmission
The USART module is configured as a Manchester encoder/decoder. Looking at the downstream communication
channel, Manchester encoded characters are serially sent to the RF emitter. This may also include a user defined
preamble and a start frame delimiter. Mostly, preamble is used in the RF receiver to distinguish between a valid
data from a transmitter and signals due to noise. The Manchester stream is then modulated. See Figure 31-18 for
an example of ASK modulation scheme. When a logic one is sent to the ASK modulator, the power amplifier,
referred to as PA, is enabled and transmits an RF signal at downstream frequency. When a logic zero is transmit-
ted, the RF signal is turned off. If the FSK modulator is activated, two different frequencies are used to transmit
data. When a logic 1 is sent, the modulator outputs an RF signal at frequency F0 and switches to F1 if the data
sent is a 0. See Figure 31-19.
From the receiver side, another carrier frequency is used. The RF receiver performs a bit check operation examin-
ing demodulated data stream. If a valid pattern is detected, the receiver switches to receiving mode. The
demodulated stream is sent to the Manchester decoder. Because of bit checking inside RF IC, the data transferred
to the microcontroller is reduced by a user-defined number of bits. The Manchester preamble length is to be
defined in accordance with the RF IC configuration.
Figure 31-18. ASK Modulator Output
LNA
VCO
RF filter
Demod
control
bi-dir
line
PA
RF filter
Mod
VCO
control
Manchester
decoder
Manchester
encoder
USART
Receiver
USART
Emitter
ASK/FSK
Upstream Receiver
ASK/FSK
downstream transmitter
Upstream
Emitter
Downstream
Receiver
Serial
Configuration
Interface
Fup frequency Carrier
Fdown frequency Carrier
Manchester
encoded
data
default polarity
unipolar output
Txd
ASK Modulator
Output
Uptstream Frequency F0
NRZ stream
10 0 1