560
32072H–AVR32–10/2012
AT32UC3A3
the Fractional Part field in BRGR (BRGR.FP), and is activated by giving it a non-zero value. The
resolution is one eighth of CD. The resulting baud rate is calculated using the following formula:
The modified architecture is shown in
.
Figure 25-14. Fractional Baud Rate Generator
25.6.4.4
Baud Rate in Synchronous and SPI Mode
If the USART is configured to operate in synchronous mode (MR.SYNC is one), the selected
clock is divided by BRGR.CD. This does not apply when the external clock CLK is selected.
When CLK is selected, the frequency of the external clock must be at least 4.5 times lower than
the system clock, and when either CLK or CLK_USART/DIV are selected, BRGR.CD must be
even to ensure a 50/50 duty cycle. If CLK_USART is selected, the generator ensures this
regardless of value.
25.6.5
RS485 Mode
The USART features an RS485 mode, supporting line driver control. This supplements normal
synchronous and asynchronous mode by driving the RTS pin high when the transmitter is oper-
ating. The RTS pin level is the inverse of the CSR.TXEMPTY value. The RS485 mode is
enabled by writing 0x1 to MR.MODE. A typical connection to a RS485 bus is shown in
BaudRate
SelectedClock
8 2
OVER
–
(
)
CD FP
8
-------
+
⎝
⎠
⎛
⎞
⎝
⎠
⎛
⎞
--------------------------------------------------------------------
=
USCLKS
CD
Modulus
Control
FP
FP
CD
glitch-free
logic
16-bit Counter
OVER
SYNC
Sampling
Divider
CLK_USART
CLK_USART/DIV
Reserved
CLK
CLK
BaudRate
Clock
Sampling
Clock
SYNC
USCLKS = 3
>1
1
2
3
0
0
1
0
1
1
0
0
BaudRate
SelectedClock
CD
--------------------------------------
=
Содержание AT32UC3A3128
Страница 61: ...61 32072H AVR32 10 2012 AT32UC3A3 PLLEN PLL Enable 0 PLL is disabled 1 PLL is enabled...
Страница 260: ...260 32072H AVR32 10 2012 AT32UC3A3 5 2560 3071 6 3072 3583 7 3584 4095 Bit Index n Sector Boundaries...
Страница 592: ...592 32072H AVR32 10 2012 AT32UC3A3 Manchester Configuration Register on page 614...
Страница 989: ...989 32072H AVR32 10 2012 AT32UC3A3 37 2 Package Drawings Figure 37 1 TFBGA 144 package drawing...
Страница 991: ...991 32072H AVR32 10 2012 AT32UC3A3 Figure 37 3 VFBGA 100 package drawing...