at91sam9g20-cu ATMEL Corporation, at91sam9g20-cu Datasheet - Page 474

• Manufacturer Part Number: at91sam9g20-cu
• Description: At91 Arm Thumb Microcontrollers
• Manufacturer: ATMEL Corporation

32.6.3.6
Figure 32-17. Manchester Encoded Characters RF Transmission
474
AT91SAM9G20 Preliminary
Downstream
Radio Interface: Manchester Encoded USART Application
Upstream
Emitter
Receiver
Fdown frequency Carrier
Fup frequency Carrier
When the start frame delimiter is a sync pattern (ONEBIT field at 0), both command and data
delimiter are supported. If a valid sync is detected, the received character is written as RXCHR
field in the US_RHR register and the RXSYNH is updated. RXCHR is set to 1 when the received
character is a command, and it is set to 0 if the received character is a data. This mechanism
alleviates and simplifies the direct memory access as the character contains its own sync field in
the same register.
As the decoder is setup to be used in unipolar mode, the first bit of the frame has to be a zero-to-
one transition.
This section describes low data rate RF transmission systems and their integration with a
Manchester encoded USART. These systems are based on transmitter and receiver ICs that
support ASK and FSK modulation schemes.
The goal is to perform full duplex radio transmission of characters using two different frequency
carriers. See the configuration in
The USART module is configured as a Manchester encoder/decoder. Looking at the down-
stream 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, pre-
amble 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
ple 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 transmitted, 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 out-
puts an RF signal at frequency F0 and switches to F1 if the data sent is a 0. See
Figure
downstream transmitter
Upstream Receiver
32-17.
RF filter
control
RF filter
control
Demod
VCO
VCO
ASK/FSK
LNA
Mod
PA
ASK/FSK
bi-dir
line
Configuration
Manchester
Manchester
decoder
encoder
Interface
Serial
Figure 32-18
Receiver
6384B–ATARM–15-Dec-08
USART
USART
Emitter
Figure
for an exam-
32-19.