222
4317I–AVR–01/08
AT90PWM2/3/2B/3B
Figure 19-6. 9 bits communication data access
19.6.2.3
UDR/EUDR data access from 13 to 17 bits per character
When the EUSART is used in 13, 14, 15, 16 or 17 bits per character mode, the EUDR/UDR reg-
isters are used in combinaison with the RxB8/TxB8 bit for data access.
For 13, 14, 15 or 16 bit character the upper unused bits in EUDR will be ignored by the Transmit-
ter and set to zero by the Receiver. In transmitter mode, the data should be written MSB first.
The data transmission starts when the UDR register is written.
In these modes, the RxB8/TxB8 registers are not used.
Figure 19-7. 13, 14, 15 and 16 bits communication data access
For 17 bit character the seventeenth bit is locate in RxB8 or TXB8 register. In transmitter mode,
the data should be written MSB first. The data transmission starts when the UDR register is
written.
Figure 19-8. 17 bits communication data access
8
7
0
Data 8:0
UDR
EUDR
8
15
7
0
Data 15:0
UDR
EUDR
8
15
16
7
0
Data 16:0
UDR
EUDR
RxB8 (receive)
or TxB8 (transmit)
