ATmega88PA Automotive Atmel Corporation, ATmega88PA Automotive Datasheet - Page 196

• Manufacturer Part Number: ATmega88PA Automotive
• Manufacturer: Atmel Corporation

20.11 Register Description
20.11.1
196
Atmel ATmega48PA/88PA/168PA [Preliminary]
UDRn – USART I/O Data Register n
Table 20-7.
The USART Transmit Data Buffer Register and USART Receive Data Buffer Registers share
the same I/O address referred to as USART Data Register or UDRn. The Transmit Data Buffer
Register (TXB) will be the destination for data written to the UDRn Register location. Reading
the UDRn Register location will return the contents of the Receive Data Buffer Register (RXB).
For 5-, 6-, or 7-bit characters the upper unused bits will be ignored by the Transmitter and set
to zero by the Receiver.
The transmit buffer can only be written when the UDREn Flag in the UCSRnA Register is set.
Data written to UDRn when the UDREn Flag is not set, will be ignored by the USART Trans-
mitter. When data is written to the transmit buffer, and the Transmitter is enabled, the
Transmitter will load the data into the Transmit Shift Register when the Shift Register is empty.
Then the data will be serially transmitted on the TxDn pin.
Max.
Note:
Bit
Read/Write
Initial Value
Baud Rate (bps)
(1)
115.2k
230.4k
14.4k
19.2k
28.8k
38.4k
57.6k
76.8k
2400
4800
9600
250k
0.5M
1M
1. UBRRn = 0, Error = 0.0%
Examples of UBRRn Settings for Commonly Used Oscillator Frequencies
(Continued)
R/W
7
0
R/W
6
0
UBRRn
416
207
103
68
51
34
25
16
12
8
3
3
1
0
R/W
U2Xn = 0
5
0
1Mbps
R/W
4
0
RXB[7:0]
TXB[7:0]
-0.1%
-0.8%
-3.5%
Error
0.2%
0.2%
0.6%
0.2%
0.2%
2.1%
0.2%
8.5%
0.0%
0.0%
0.0%
f
osc
R/W
3
0
= 16.0000MHz
R/W
2
0
UBRRn
832
416
207
138
103
68
51
34
25
16
8
7
3
1
R/W
1
0
U2Xn = 1
2Mbps
R/W
0
0
9223B–AVR–09/11
UDRn (Read)
UDRn (Write)
-0.1%
-0.1%
-0.8%
-3.5%
Error
0.0%
0.2%
0.2%
0.6%
0.2%
0.2%
2.1%
0.0%
0.0%
0.0%