AT32UC3C2512C Automotive Atmel Corporation, AT32UC3C2512C Automotive Datasheet - Page 570

• Manufacturer Part Number: AT32UC3C2512C Automotive
• Manufacturer: Atmel Corporation

25.6.2
9166C–AVR-08/11
Receiver and Transmitter Control
Generator Register (BRGR). The resulting clock can be provided to the CLK pin to feed the
smart card clock inputs. This means that the CLKO bit can be set in MR.
This clock is then divided by the value programmed in the FI_DI_RATIO field in the FI_DI_Ratio
register (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 25-4
and the ISO 7816 clock.
Figure 25-4. Elementary Time Unit (ETU)
After reset, the receiver is disabled. The user must enable the receiver by setting the RXEN bit
in the Control Register (CR). However, the receiver registers can be programmed before the
receiver clock is enabled.
After reset, the transmitter is disabled. The user must enable it by setting the TXEN bit in the
Control Register (CR). However, the transmitter registers can be programmed before being
enabled.
The Receiver and the Transmitter can be enabled together or independently.
At any time, the software can perform a reset on the receiver or the transmitter of the USART by
setting the corresponding bit, RSTRX and RSTTX respectively, in the Control Register (CR).
The software resets clear the status flag and reset internal state machines but the user interface
configuration registers hold the value configured prior to software reset. Regardless of what the
receiver or the transmitter is performing, the communication is immediately stopped.
The user can also independently disable the receiver or the transmitter by setting RXDIS and
TXDIS respectively in CR. If the receiver is disabled during a character reception, the USART
waits until the end of reception of the current character, then the reception is stopped. If the
transmitter is disabled while it is operating, the USART waits the end of transmission of both the
current character and character being stored in the Transmit Holding Register (THR). If a time-
guard is programmed, it is handled normally.
ISO7816 I/O Line
ISO7816 Clock
shows the relation between the Elementary Time Unit, corresponding to a bit time,
on TXD
on CLK
ISO7816 Clock Cycles
FI_DI_RATIO
1 ETU
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