Datasheet
564
32072H–AVR32–10/2012
AT32UC3A3
• 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 25-9.
Fi is a binary value encoded on a 4-bit field, named FI, as represented in Table 25-10.
Table 25-11 shows the resulting Fi/Di ratio, which is the ratio between the ISO7816 clock and
the Baud Rate Clock.
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 25-21 shows the
relationship between the Elementary Time Unit (ETU), corresponding to a bit period, and the
ISO 7816 clock.
Table 25-9. Binary and Decimal Values for Di
DI field 0001 0010 0011 0100 0101 0110 1000 1001
Di (decimal)1 2 4 8 163212 20
Table 25-10. Binary and Decimal Values for Fi
FI field 0000 0001 0010 0011 0100 0101 0110 1001 1010 1011 1100 1101
Fi (decimal 372 372 558 744 1116 1488 1860 512 768 1024 1536 2048
Table 25-11. 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