at43usb320a ATMEL Corporation, at43usb320a Datasheet - Page 63

• Manufacturer Part Number: at43usb320a
• Description: Full-speed Usb Microcontroller With An Embedded Hub
• Manufacturer: ATMEL Corporation

Baud Rate
Generator
UART BAUD Rate
Register
I/O-Ports
Port A
1443E–USB–4/04
–
UBRR
The baud rate generator is a frequency divider that generates baud rates according to the fol-
lowing equation:
BAUD = SYSCLK/16(UBRR + 1)
• BAUD = Baud rate
• SYSCLK = 16 MHz
• UBRR = Contents of the UART Baud Rate register, UBRR (0
For standard crystal frequencies, the most commonly used baud rates can be generated by
using the UBRR settings in Table 22. UBRR values that yield an actual baud rate differing less
than 2% from the target baud rate are boldface in the table. However, using baud rates that
have more than 1% error is not recommended. High error ratings give less noise immunity.
Table 22. UBRR Settings
The UBRR register is an 8-bit read/write register that specifies the UART Baud Rate according
to the equation on the previous page.
All AVR ports have true Read-Modify-Write functionality when used as general digital I/O
ports. This means that the direction of one port pin can be changed without unintentionally
changing the direction of any other pin with the SBI and CBI instructions. The same applies for
changing drive value if configured as output or enabling/disabling of pull-up resistors if config-
ured as input.
Port A is an 8-bit bi-directional I/O port. The Port A output buffers can sink or source 4 mA
Three I/O memory address locations are allocated for the Port A, one each for the Data Regis-
ter PORTA, $1B($3B), Data Direction Register (DDRA), $1A($3A) and the Port A Input Pins
Baud Rate
2400
4800
9600
14400
19200
28800
38400
57600
76800
115200
Read/Write
Initial value
$09 ($29)
Bit
MSB
R/W
7
0
R/W
6
0
UBRR
416
207
103
68
51
34
25
16
12
8
R/W
5
0
R/W
4
0
R/W
3
0
R/W
2
0
% Error
0.08
0.16
0.16
0.64
0.16
0.79
0.16
2.12
0.16
3.55
AT43USB320A
–
255)
R/W
1
0
LSB
R/W
0
0
UBRR
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