308
8331B–AVR–03/12
Atmel AVR XMEGA AU
If the receiver is set up to receive frames that contain five to eight data bits, the first stop bit is
used to indicate the frame type. If the receiver is set up for frames with nine data bits, the ninth
bit is used. When the frame type bit is one, the frame contains an address. When the frame type
bit is zero, the frame is a data frame. If 5-bit to 8-bit character frames are used, the transmitter
must be set to use two stop bits, since the first stop bit is used for indicating the frame type.
If a particular slave MCU has been addressed, it will receive the following data frames as usual,
while the other slave MCUs will ignore the frames until another address frame is received.
23.12.1
Using Multiprocessor Communication Mode
The following procedure should be used to exchange data in multiprocessor communication
mode (MPCM):
1.
All slave MCUs are in multiprocessor communication mode.
2.
The master MCU sends an address frame, and all slaves receive and read this frame.
3.
Each slave MCU determines if it has been selected.
4.
The addressed MCU will disable MPCM and receive all data frames. The other slave
MCUs will ignore the data frames.
5.
When the addressed MCU has received the last data frame, it must enable MPCM
again and wait for a new address frame from the master.
The process then repeats from step 2.
Using any of the 5-bit to 8-bit character frame formats is impractical, as the receiver must
change between using n and n+1 character frame formats. This makes full-duplex operation dif-
ficult, since the transmitter and receiver must use the same character size setting.
23.13 IRCOM Mode of Operation
IRCOM mode can be enabled to use the IRCOM module with the USART. This enables IrDA 1.4
compliant modulation and demodulation for baud rates up to 115.2kbps. When IRCOM mode is
enabled, double speed mode cannot be used for the USART.
For devices with more than one USART, IRCOM mode can be enabled for only one USART at a
time. For details, refer to
”IRCOM - IR Communication Module” on page 316
23.14 DMA Support
DMA support is available on UART, USRT, and master SPI mode peripherals. For details on dif-
ferent USART DMA transfer triggers, refer to