AT91SAM7S32-AI ATMEL [ATMEL Corporation], AT91SAM7S32-AI Datasheet - Page 271

• Manufacturer Part Number: AT91SAM7S32-AI
• Description: AT91 ARM Thumb-based Microcontrollers
• Manufacturer: ATMEL [ATMEL Corporation]

Table 59. Baud Rate Example (OVER = 0) (Continued)
Baud Rate in
Synchronous Mode
Baud Rate in ISO 7816
Mode
6071A–ATARM–28-Oct-04
Source Clock
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
60 000 000
70 000 000
Expected Baud
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%.
If the USART is programmed to operate in synchronous mode, the selected clock is simply
divided by the field CD in US_BRGR.
In synchronous mode, if the external clock is selected (USCLKS = 3), the clock is provided
directly by the signal on the USART SCK pin. No division is active. The value written in
US_BRGR has no effect. The external clock frequency must be at least 4.5 times lower than
the system clock.
When either the external clock SCK or the internal clock divided (MCK/DIV) is selected, the
value programmed in CD must be even if the user has to ensure a 50:50 mark/space ratio on
the SCK pin. If the internal clock MCK is selected, the Baud Rate Generator ensures a 50:50
duty cycle on the SCK pin, even if the value programmed in CD is odd.
The ISO7816 specification defines the bit rate with the following formula:
where:
•
•
•
•
38 400
38 400
38 400
38 400
38 400
38 400
38 400
38 400
38 400
38 400
38 400
Rate
BaudRate
Error
BaudRate
B is the bit rate
Di is the bit-rate adjustment factor
Fi is the clock frequency division factor
f is the ISO7816 clock frequency (Hz)
B
=
=
1
Di
----- -
Fi
=
–
=
⎛
SelectedClock
------------------------------------- -
Calculation Result
ExpectedBaudRate
-------------------------------------------------- -
f
MCK CD
ActualBaudRate
CD
113.93
30.00
39.06
40.00
40.69
52.08
53.33
53.71
65.10
81.38
97.66
16
⎞
⎠
114
CD
30
39
40
40
52
53
54
65
81
98
AT91SAM7S32 Preliminary
Actual Baud Rate
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
38 265.31
38 377.19
0.00%
0.16%
0.00%
0.76%
0.16%
0.63%
0.54%
0.16%
0.47%
0.35%
0.06%
Error
271