AT91SAM7S256D-AU Atmel, AT91SAM7S256D-AU Datasheet - Page 368

• 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 31-4.
Table 31-5.
FI field
Fi (decimal
Fi/Di
16
32
12
20
1
2
4
8
Fi is a binary value encoded on a 4-bit field, named FI, as represented in
Table 31-5
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 supported 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 31-7
clock.
Figure 31-7. Elementary Time Unit (ETU)
23.25
11.62
46.5
18.6
Binary and Decimal Values for Fi
Possible Values for the Fi/Di Ratio
372
372
186
0000
93
31
372
shows the resulting Fi/Di Ratio, which is the ratio between the ISO7816 clock and the baud rate clock.
shows the relation between the Elementary Time Unit, corresponding to a bit time, and the ISO 7816
ISO7816 I/O Line
0001
139.5
69.75
34.87
17.43
372
46.5
27.9
558
558
279
ISO7816 Clock
on SCK
on TXD
0010
558
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
0100
1116
1488
1488
46.5
74.4
744
372
186
124
93
0101
1488
232.5
116.2
58.13
1806
1860
ISO7816 Clock Cycles
930
465
155
93
FI_DI_RATIO
0110
1860
1 ETU
42.66
25.6
512
512
256
128
64
32
16
1001
512
Table
SAM7S Series [DATASHEET]
38.4
768
768
384
192
96
48
24
64
31-4.
1010
768
85.33
1024
1024
51.2
512
256
128
64
32
1011
1024
6175M–ATARM–26-Oct-12
1536
1536
76.8
768
384
192
128
1100
1536
48
96
170.6
102.4
2048
2048
2048
1024
1101
512
256
128
64
368