Datasheet

SAM9G20
DS60001516A-page 470  2017 Microchip Technology Inc.
Figure 31-35: IrDA Demodulator Operations
As the IrDA mode uses the same logic as the ISO7816, note that the FI_DI_RATIO field in US_FIDI must be set to a value higher than 0
in order to assure IrDA communications operate correctly.
31.6.6 RS485 Mode
The USART features the RS485 mode to enable line driver control. While operating in RS485 mode, the USART behaves as though in
asynchronous or synchronous mode and configuration of all the parameters is possible. The difference is that the RTS pin is driven high
when the transmitter is operating. The behavior of the RTS pin is controlled by the TXEMPTY bit. A typical connection of the USART to a
RS485 bus is shown in Figure 31-36.
Figure 31-36: Typical Connection to a RS485 Bus
The USART is set in RS485 mode by programming the USART_MODE field in the Mode Register (US_MR) to the value 0x1.
The RTS pin is at a level inverse to the TXEMPTY bit. Significantly, the RTS pin remains high when a timeguard is programmed so that
the line can remain driven after the last character completion. Figure 31-37 gives an example of the RTS waveform during a character
transmission when the timeguard is enabled.
MCK
RXD
Receiver
Input
Pulse
Rejected
6543 2 6
1
6543 2 0
Pulse
Accepted
Counter
Value
USART
RTS
TXD
RXD
Differential
Bus