Irda Sir Endec Block - STMicroelectronics STM32F05 series Reference Manual

RM0091
Therefore, two methods are available for TS pattern recognition:
Method 1: The USART is programmed in standard Smartcard mode/direct convention. In
this case, the TS pattern reception generates a parity error interrupt and error signal to the
card.
●
The parity error interrupt informs the software that the card didn't answer correctly in
direct convention. Software then reprograms the USART for inverse convention
●
In response to the error signal, the card retries the same TS character, and it will be
correctly received this time, by the reprogrammed USART
Alternatively, in answer to the parity error interrupt, the software may decide to reprogram
the USART and to also generate a new reset command to the card, then wait again for the
TS.
Method 2: The USART is programmed in 9-bit/no-parity mode, no bit inversion. In this mode
it receives any of the two TS patterns as:
(H) LHHL LLL LLH = 0x103 -> inverse convention to be chosen
(H) LHHL HHH LLH = 0x13B -> direct convention to be chosen
The software checks the received character against these two patterns and, if any of them
match, then programs the USART accordingly for the next character reception.
If none of the two is recognized, a card reset may be generated in order to restart the
negotiation.
25.5.14

IrDA SIR ENDEC block

This section is relevant only when IrDA mode is supported. Please refer to
USART implementation on page
IrDA mode is selected by setting the IREN bit in the USART_CR3 register. In IrDA mode, the
following bits must be kept cleared:
● LINEN, STOP and CLKEN bits in the USART_CR2 register,
●
SCEN and HDSEL bits in the USART_CR3 register.
The IrDA SIR physical layer specifies use of a Return to Zero, Inverted (RZI) modulation
scheme that represents logic 0 as an infrared light pulse (see
The SIR Transmit encoder modulates the Non Return to Zero (NRZ) transmit bit stream
output from USART. The output pulse stream is transmitted to an external output driver and
infrared LED. USART supports only bit rates up to 115.2 Kbps for the SIR ENDEC. In
normal mode the transmitted pulse width is specified as 3/16 of a bit period.
The SIR receive decoder demodulates the return-to-zero bit stream from the infrared
detector and outputs the received NRZ serial bit stream to the USART. The decoder input is
normally high (marking state) in the Idle state. The transmit encoder output has the opposite
polarity to the decoder input. A start bit is detected when the decoder input is low.
●
IrDA is a half duplex communication protocol. If the Transmitter is busy (when the
USART is sending data to the IrDA encoder), any data on the IrDA receive line is
ignored by the IrDA decoder and if the Receiver is busy (when the USART is receiving
decoded data from the USART), data on the TX from the USART to IrDA is not
Universal synchronous asynchronous receiver transmitter (USART)
573.
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Section 25.4:
Figure 245).
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