AT91SAM7S32-AI ATMEL [ATMEL Corporation], AT91SAM7S32-AI Datasheet - Page 272

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

Table 60. Binary and Decimal Values for D
Table 61. Binary and Decimal Values for F
Table 62. Possible Values for the Fi/Di Ratio
272
DI field
Di (decimal)
FI field
Fi (decimal
Fi/Di
16
32
12
20
1
2
4
8
AT91SAM7S32 Preliminary
23.25
11.62
46.5
18.6
372
372
186
0000
93
31
372
0001
1
0001
139.5
69.75
34.87
17.43
372
46.5
27.9
558
558
279
Di is a binary value encoded on a 4-bit field, named DI, as represented in Table 60.
Fi is a binary value encoded on a 4-bit field, named FI, as represented in Table 61.
Table 62 shows the resulting Fi/Di Ratio, which is the ratio between the ISO7816 clock and the
baud rate clock.
If the USART is configured in ISO7816 Mode, the clock selected by the USCLKS field in the
Mode Register (US_MR) is first divided by the value programmed in the field CD in the Baud
Rate Generator Register (US_BRGR). The resulting clock can be provided to the SCK pin to
feed the smart card clock inputs. This means that the CLKO bit can be set in US_MR.
This clock is then divided by the value programmed in the FI_DI_RATIO field in the
FI_DI_Ratio register (US_FIDI). This is performed by the Sampling Divider, which performs a
division by up to 2047 in ISO7816 Mode. The non-integer values of the Fi/Di Ratio are not sup-
ported and the user must program the FI_DI_RATIO field to a value as close as possible to the
expected value.
The FI_DI_RATIO field resets to the value 0x174 (372 in decimal) and is the most common
divider between the ISO7816 clock and the bit rate (Fi = 372, Di = 1).
Figure 103 shows the relation between the Elementary Time Unit, corresponding to a bit time,
and the ISO 7816 clock.
0010
0010
558
2
23.25
46.5
37.2
774
744
372
186
93
62
0011
744
139.5
69.75
34.87
1116
1116
55.8
558
279
93
0011
4
0100
1116
1488
1488
46.5
74.4
744
372
186
124
93
0100
0101
1488
8
232.5
58.13
116.2
1806
1860
930
465
155
93
1860
0110
0101
16
42.66
25.6
256
128
512
512
64
32
16
1001
512
38.4
0110
768
768
384
192
96
48
24
64
32
1010
768
85.33
1024
1024
51.2
512
256
128
64
32
1024
1011
1000
12
6071A–ATARM–28-Oct-04
1536
1536
76.8
768
384
192
128
1100
1536
96
48
1001
20
170.6
102.4
1101
2048
2048
2048
1024
512
256
128
64