Atmel ARM-Based Evaluation Kit for SAM4S16C, 32-Bit ARM® Cortex® Microcontroller ATSAM4S-WPIR-RD ATSAM4S-WPIR-RD Data Sheet

SAM4S Series [DATASHEET]

Atmel-11100G-ATARM-SAM4S-Datasheet_27-May-14

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The USART peripheral 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 

 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 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 outputs an RF signal at frequency F0 and switches to F1 if 

the data sent is a 0. See 

.

From the receiver side, another carrier frequency is used. The RF receiver performs a bit check operation 

examining 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.

In synchronous mode (SYNC = 1), the receiver samples the RXD signal on each rising edge of the baud rate clock. 

If a low level is detected, it is considered as a start. All data bits, the parity bit and the stop bits are sampled and the 

receiver waits for the next start bit. Synchronous mode operations provide a high-speed transfer capability.
Configuration fields and bits are the same as in asynchronous mode.

 illustrates a character reception in synchronous mode.

Manchester

encoded

data

default polarity

unipolar output

Txd

ASK Modulator

Output

Uptstream Frequency F0

NRZ stream

1

0

0

1

Manchester

encoded

data

default polarity

unipolar output

Txd

FSK Modulator

Output

Uptstream Frequencies 

[F0, F0+offset]

NRZ stream

1

0

0

1