DocID024597 Rev 3 1213/1693
RM0351 Universal synchronous asynchronous receiver transmitter (USART)
1282
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 USARTx_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 400. IrDA SIR ENDEC- block diagram
Figure 401. IrDA data modulation (3/16) -Normal Mode
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