參數資料
型號: AT91M40807-33AI
廠商: ATMEL CORP
元件分類: 微控制器/微處理器
英文描述: Microcontroller
中文描述: 32-BIT, MROM, 33 MHz, RISC MICROCONTROLLER, PQFP100
封裝: 1.40 MM HEIGHT, TQFP-100
文件頁數: 100/153頁
文件大小: 1837K
代理商: AT91M40807-33AI
100
AT91X40 Series
1354D
ATARM
05/02
Baud Rate Generator
The Baud Rate Generator provides the bit period clock (the Baud Rate clock) to both the
Receiver and the Transmitter.
The Baud Rate Generator can select between external and internal clock sources. The
external clock source is SCK. The internal clock sources can be either the master clock
(MCK) or the master clock divided by 8 (MCK/8).
Note:
In all cases, if an external clock is used, the duration of each of its levels must be longer
than the system clock (MCK) period. The external clock frequency must be at least 2.5
times lower than the system clock.
When the USART is programmed to operate in Asynchronous Mode (SYNC = 0 in the
Mode Register US_MR), the selected clock is divided by 16 times the value (CD) written
in US_BRGR (Baud Rate Generator Register). If US_BRGR is set to 0, the Baud Rate
Clock is disabled.
When the USART is programmed to operate in Synchronous Mode (SYNC = 1) and the
selected clock is internal (USCLKS[1] = 0 in the Mode Register US_MR), the Baud Rate
Clock is the internal selected clock divided by the value written in US_BRGR. If
US_BRGR is set to 0, the Baud Rate Clock is disabled.
In Synchronous Mode with external clock selected (USCLKS[1] = 1), the clock is pro-
vided directly by the signal on the SCK pin. No division is active. The value written in
US_BRGR has no effect.
Figure 37.
Baud Rate Generator
Baud Rate
=
Selected Clock
16 x CD
Baud Rate
=
Selected Clock
CD
USCLKS [1]
0
0
1
1
MCK
MCK/8
SCK
CLK
16-bit Counter
0
0
1
Baud Rate
Clock
SYNC
USCLKS [1]
CD
CD
OUT
0
1
Divide
by 16
SYNC
0
1
>1
USCLKS [0]
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