AT91SAM7S256D-AU Atmel, AT91SAM7S256D-AU Datasheet - Page 366

• Manufacturer Part Number: AT91SAM7S256D-AU
• Description: ARM Microcontrollers - MCU 256K Flash SRAM 64K ARM based MCU
• Manufacturer: Atmel
• Series: SAM7S256r

Specifications of AT91SAM7S256D-AU

• Rohs: yes
• Core: ARM
• Processor Series: AT91SAM
• Data Bus Width: 16 bit/32 bit
• Maximum Clock Frequency: 55 MHz
• Program Memory Size: 256 KB
• Data Ram Size: 64 KB
• On-chip Adc: Yes
• Operating Supply Voltage: 3 V to 3.6 V
• Operating Temperature Range: - 40 C to + 85 C
• Package / Case: LQFP-64
• Mounting Style: SMD/SMT
• Interface Type: 2-Wire, I2S, SPI, USART
• Length: 7 mm

Table 31-2.
31.6.1.3
Source Clock
14 745 600
18 432 000
24 000 000
24 576 000
25 000 000
32 000 000
32 768 000
33 000 000
40 000 000
50 000 000
The baud rate is calculated with the following formula:
The baud rate error is calculated with the following formula. It is not recommended to work with an error higher than
5%.
The Baud Rate generator previously defined is subject to the following limitation: the output frequency changes by
only integer multiples of the reference frequency. An approach to this problem is to integrate a fractional N clock
generator that has a high resolution. The generator architecture is modified to obtain Baud Rate changes by a frac-
tion of the reference source clock. This fractional part is programmed with the FP field in the Baud Rate Generator
Register (US_BRGR). If FP is not 0, the fractional part is activated. The resolution is one eighth of the clock divider.
This feature is only available when using USART normal mode. The fractional Baud Rate is calculated using the
following formula:
The modified architecture is presented below:
Baudrate
BaudRate
Error
SAM7S512/156/128 Fractional Baud Rate in Asynchronous Mode
Baud Rate Example (OVER = 0) (Continued)
=
=
1
------------------------------------------------------------------
⎛
⎝
–
8 2 Over
⎛
⎝
(
=
Expected Baud
ExpectedBaudRate
-------------------------------------------------------- -
SelectedClock
ActualBaudRate
–
MCK
38 400
38 400
38 400
38 400
38 400
38 400
38 400
38 400
38 400
38 400
Rate
⁄
) CD
⎛
⎝
CD
+
×
FP
------- -
16
8
Calculation Result
⎞
⎠
⎞
⎠
⎞
⎠
24.00
30.00
39.06
40.00
40.69
52.08
53.33
53.71
65.10
81.38
CD
24
30
39
40
40
52
53
54
65
81
Actual Baud Rate
SAM7S Series [DATASHEET]
38 400.00
38 400.00
38 461.54
38 400.00
38 109.76
38 461.54
38 641.51
38 194.44
38 461.54
38 580.25
6175M–ATARM–26-Oct-12
0.00%
0.00%
0.16%
0.00%
0.76%
0.16%
0.63%
0.54%
0.16%
0.47%
Error
366