AN2646 datasheet(5/43 Pages) STMICROELECTRONICS

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AN2646 - Application note

Smartcard interface description

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to the card. The length of an ETU is a bit time. The UART1 transmitter output and receiver

input are internally connected through the Rx_SW line. For the transmission of data from the

STM8S20x to the smartcard, the UART1 must be set up in smartcard mode.

Figure 1.

ISO 7816-3 asynchronous protocol

1.4

Smartcard clock generator

The smartcard clock generator provides a clock signal to the connected smartcard. The

smartcard uses this clock to derive the baud rate clock for the serial I/O between the

smartcard and another UART1. The clock is also used for the CPU in the card, if present.

Operation of the smartcard interface requires that the clock rate to the card is adjusted while

the CPU in the card is running code so that the baud rate can be changed or the

performance of the card can be increased. The protocols that govern the negotiation of

these clock rates and the altering of the clock rate are detailed in the ISO 7816-3 standard.

The clock is used as the CPU clock for the smartcard, therefore updates to the

microcontroller clock rate must be synchronized to the smartcard clock, that is the clock high

or low pulse widths must not be shorter than either the old or new programmed value.

AN2646 Datasheet(PDF) 5 Page - STMicroelectronics