SAM4L Datasheet, PDF (610/1185 Pages) ATMEL Corporation – ATSAM ARM-based Flash MCU

ATSAM4L4/L2
Figure 24-50. Manchester Error
Preamble Length
is set to 4
Manchester
encoded
data ^Txd
sampling points
SFD
Elementary character bit time
Entering USART character area
Preamble subpacket
and Start Frame Delimiter
were successfully
decoded
Manchester
Coding Error
detected
24.6.16.3
Radio Interface: Manchester Endec Application
This section describes low data rate, full duplex, dual frequency, RF systems integrated with a
Manchester endec, that support ASK and/or FSK modulation schemes. See Figure 24-51.
Figure 24-51. Manchester Encoded Characters RF Transmission
Fup frequency Carrier
Upstream
Emitter
ASK/FSK
Upstream Receiver
LNA
VCO
RF filter
Demod
Serial
Configuration
Interface
Fdown frequency Carrier
Downstream
Receiver
control
bi-dir
line
ASK/FSK
downstream transmitter
PA
RF filter
Mod
VCO
Manchester
decoder
USART
Receiver
Manchester
encoder
USART
Emitter
control
To transmit downstream, encoded data is sent serially to the RF modulator and then through
space to the RF receiver. To receive, another frequency carrier is used and the RF demodulator
does a bit-checking search for valid patterns before it switches to a receiving mode and forwards
data to the decoder. Defining preambles to help distinguish between noise and valid data has to
be done in conjunction with the RF module, and may sometimes be filtered away from the endec
stream. Using the ASK modulation scheme, a one is transmitted as an RF signal at the down-
stream frequency, while a zero is transmitted as no signal. See Figure 24-52. The FSK
modulation scheme uses two different frequencies to transmit data. A one is sent as a signal on
one frequency, and a zero on the other. See Figure 24-53.
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