RM0082
LS_Fast IrDA controller
Doc ID 018672 Rev 1
573/844
reset the bit RXS of the IrDA_STAT register. At last, a frame invalid interrupt (FI_INT,
) is generated. This behaviour allows to handle the case of a frame abort.
Note:
The used reception abort timer has to be programmed via the field RATV of the
configuration register IrDA_CONF (
).
26.3.2 Demodulation
unit
The demodulation unit is active in the reception state only, and it is responsible for the
demodulation of the synchronized active high RX signal from the synchronization unit in
order to obtain the RX frame. The actual demodulation performed by this unit depends on
the infrared mode (SIR, MIR or FIR).
Note:
The POLRX bit in the IrDA_CONF register (
) must be set according to the
polarity of the RX signal.
SIR and MIR (RIZ demodulation)
At first, the demodulation unit extends the pulse of the synchronized active high RX signal in
order to avoid jitter influences. Then the obtained signal is then sampled by the
en_symb
signal (from the baud rate generation unit,
Section 26.3.5: Baud rate generation unit on
) to get the RX frame for wrapper unit.
The
en_symb
signal has a phase determinated by the first rising edge of the incoming RX
signal and is checked (re-adjusted, if needed) every following rising edge.
FIR (4PPM demodulation)
The preamble field PA of the synchronized RX signal is used by the receiver to establish
phase lock by means of a DPLL (digital phase locked loop). Then the incoming signal is
sampled with the recovered enable signal
en_pulse
. To establish symbol synchronization
the receiver, during PA, begins to search for the start flag STA. When it is received correctly
the received starts to demodulate the RX frame and generates a frame detected interrupt
(FD_INT,
) until the stop flag STOP, which indicates the end of the frame, is
recognized.
26.3.3 Wrapper
unit
The wrapper unit is active in transmission and reception states only.
Reception state
The wrapper unit retrieves the IrLAP frame and the CRC bytes out of the RX frame from
demodulation unit. The decoding mode depends on the used infrared mode, which is
determined by the 2 bit field MODE of the parameter register IrDA_PARA (
).
After decoding, the IrLAP and CRC bytes are shifted into the FIFO unit. If an error is
detected either in the demodulation unit or in FIFO Unit, the decoding process is aborted.
Transmission state
The
wrapper unit
builds the TX frame out of IrLAP frame which should be transmitted. The
TX frame is then sent (LSB first) to the modulation unit. The encoding mode depends on the
used infrared mode, which is determined by the 2 bit field MODE of the parameter register
IrDA_PARA (