RM0319 datasheet(248/368 Pages) STMICROELECTRONICS

248 / 368 page

Fast infrared port (IRDA)

RM0319

248/368

Doc ID 022640 Rev 3

Besides, if the synchronization unit detects no activity of the RX signal for more than 10 ms

when in reception state, the FIrDA controller switches back to the listening state and resets

the bit RXS of the IrDA_STAT register. At last, a frame invalid interrupt (FI_INT, Section 19.4)

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.

19.3.2

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 (RZI demodulation)

In SIR mode, RZI (Return-to-Zero-Inverted) modulation is used. This means that for a "0" bit

in the TX (RX) frame a high pulse is generated and for a "1" bit in the TX (RX) frame no

pulse is generated.

For example, the byte to be transmitted is 0x6C, then 01101100 is shifted into the

Modulation Unit, LSB first.

MIR mode also uses RZI modulation, but the pulse length is 1/4 of a bit.

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 19.3.5: Baud rate generation unit on

page 250) to get the RX frame for wrapper unit.

The en_symb signal has a phase determined by the first rising edge of the incoming RX

signal and is checked (re-adjusted, if needed) every following rising edge.

FIR (4PPM demodulation)

In FIR mode, Four Pulse Position Modulation (4PPM) is used to modulate the TX frame.

Additionally a preamble PA, a start flag STA and a stop flag STO are added as shown in

Figure 88.

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