DocID024597 Rev 5 1337/1830
RM0351 Universal synchronous asynchronous receiver transmitter (USART)
1411
• The IrDA specification requires the acceptance of pulses greater than 1.41 µs. The
acceptable pulse width is programmable. Glitch detection logic on the receiver end
filters out pulses of width less than 2 PSC periods (PSC is the prescaler value
programmed in the USART_GTPR). Pulses of width less than 1 PSC period are always
rejected, but those of width greater than one and less than two periods may be
accepted or rejected, those greater than 2 periods will be accepted as a pulse. The
IrDA encoder/decoder doesn’t work when PSC=0.
• The receiver can communicate with a low-power transmitter.
• In IrDA mode, the STOP bits in the USART_CR2 register must be configured to “1 stop
bit”.
IrDA low-power mode
Transmitter
In low-power mode the pulse width is not maintained at 3/16 of the bit period. Instead, the
width of the pulse is 3 times the low-power baud rate which can be a minimum of 1.42 MHz.
Generally, this value is 1.8432 MHz (1.42 MHz < PSC< 2.12 MHz). A low-power mode
programmable divisor divides the system clock to achieve this value.
Receiver
Receiving in low-power mode is similar to receiving in normal mode. For glitch detection the
USART should discard pulses of duration shorter than 1 PSC period. A valid low is accepted
only if its duration is greater than 2 periods of the IrDA low-power Baud clock (PSC value in
the USART_GTPR).
Note: A pulse of width less than two and greater than one PSC period(s) may or may not be
rejected.
The receiver set up time should be managed by software. The IrDA physical layer
specification specifies a minimum of 10 ms delay between transmission and reception (IrDA
is a half duplex protocol).
Figure 423. IrDA SIR ENDEC- block diagram
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