RM0319 datasheet(249/368 Pages) STMICROELECTRONICS

249 / 368 page

RM0319

Fast infrared port (IRDA)

Doc ID 022640 Rev 3

249/368

Figure 88.

Tx signal generation at 4 Mbps in FIR mode

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, Section 19.4) until the stop flag STOP, which indicates the end of the frame, is

recognized.

4PPM encoding is achieved by defining a data symbol duration (tFIRsymb) and subsequently

subdividing tFIRsymb into four equal time slices tFIRpw.

tFIRpw marks the time space when an infrared pulse can be sent. Within a data symbol only

one pulse is allowed, thus there exist four different data symbols, which represent the four

possible combinations of two bits. The used data symbols are listed in Table 70 with the

corresponding data bit pairs.

19.3.3

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.

Table 70.

4PPM encoding scheme

Data bit pair

MSB LSB

4PPM data symbol

sent first…last

1000

0100

0010

0001

IrLAP Frame + CRC32

Tx Frame

Preamble

Start flag

Stop flag

4PPM modulated Tx Frame

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