SAM4L Datasheet, PDF (587/1185 Pages) ATMEL Corporation – ATSAM ARM-based Flash MCU

ATSAM4L4/L2
• 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)
Di is a binary value encoded on a 4-bit field, named DI, as represented in Table 24-9.
Table 24-9. Binary and Decimal Values for Di
DI field
0001
0010
0011
Di (decimal)
1
2
4
0100
8
0101
16
0110
32
1000
12
1001
20
Fi is a binary value encoded on a 4-bit field, named FI, as represented in Table 24-10.
Table 24-10. Binary and Decimal Values for Fi
FI field
0000 0001 0010 0011
Fi (decimal 372
372
558
744
0100
1116
0101
1488
0110
1860
1001
512
1010
768
1011
1024
1100
1536
1101
2048
Table 24-11 shows the resulting Fi/Di ratio, which is the ratio between the ISO7816 clock and
the Baud Rate Clock.
Table 24-11. Possible Values for the Fi/Di Ratio
Fi
372
558
744
1116
1488
1860
512
768
1024
1536
2048
Di=2
186
279
372
558
744
930
256
384
512
768
1024
Di=4
93
139.5
186
279
372
465
128
192
256
384
512
Di=8
46.5
69.75
93
139.5
186
232.5
64
96
128
192
256
Di=16
23.25
34.87
46.5
69.75
93
116.2
32
48
64
96
128
Di=32
11.62
17.43
23.25 34.87
46.5
58.13
16
24
32
48
64
Di=12
31
46.5
62
93
124
155
42.66
64
85.33
128
170.6
Di=20
18.6
27.9
37.2
55.8
74.4
93
25.6
38.4
51.2
76.8
102.4
The clock selected by MR.USCLKS can be output on the CLK pin to feed the smart card clock
inputs. To output the clock, the user must write a one to the Clock Output Select bit in MR
(MR.CLKO). The clock is divided by BRGR.CD before it is output on the CLK pin. If CLK is
selected as clock source in MR.USCLKS, the clock can not be output on the CLK pin.
The selected clock is divided by the FI Over DI Ratio Value field in the FI DI Ratio Register
(FIDI.FI_DI_RATIO), which can be up to 2047 in ISO7816 mode. This will be rounded off to an
integral so the user has to select a FI_DI_RATIO value that comes as close as possible to the
expected Fi/Di ratio. The FI_DI_RATIO reset value is 0x174 (372 in decimal) and is the most
common divider between the ISO7816 clock and bit rate (Fi=372, Di=1). Figure 24-21 shows the
relationship between the Elementary Time Unit (ETU), corresponding to a bit period, and the
ISO 7816 clock.
42023C–SAM–02/2013
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