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Smartcard interface description

AN2646 - Application note

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Smartcard interface description

1.1

Introduction

The smartcard interface is developed using the UART1 smartcard mode. For the description

of the UART1 registers, please refer to the STM8S/STM8A reference manual (RM0009).

The UART1 smartcard mode supports asynchronous protocol smartcards as defined in the

ISO 7816-3 (Class A) standard, please refer to the ISO 7816-3 specification for more

details.

With the smartcard mode enabled, the UART1 must be configured as:

●

Eight data bits plus parity

●

0.5 or 1.5 stop bits

A 5-bit prescaler and the smartcard clock generator provide the clock to the smartcard.

GPIO pins in conjunction with software are used to provide the rest of the functions required

to interface to the smartcard.

The inverse signalling convention as defined in ISO 7816-3, inverted data and MSB first, is

not handled in the software.

There are three types of card that operate at different voltages:

●

5V (ISO7816-3 Class A)

●

3V (ISO7816-3 Class B)

●

1.8V (ISO7816-3 Class C)

1.2

External interface

The Smartcard_RST (Smartcard reset), Smartcard_3/5V (3 V or 5 V), Smartcard_CMDVCC

(command for VCC), and Smartcard_OFF signals (signal for card detection) are provided by

GPIO bits of the I/O ports under software control. Programming the GPIO bits of the port for

alternate function open-drain mode connects the UART1_TX data signal to the

Smartcard_IO pin with the correct driver type and the clock generator to the

Smartcard_CLK pin configured in output push-pull.

1.3

Protocol

The ISO 7816-3 standard defines the bit times for the asynchronous protocol in terms of

time units called ETUs (elementary time units), that are related to the clock frequency input

Table 1.

Smartcard pins

STM8S20x pin

Smartcard pin

Function

UART1_CK

CLK

Smartcard clock

UART1_TX

IO serial data: open drain

Any GPIO

RST

Reset to card

Any GPIO

VCC

Supply voltage

Any GPIO

VPP

Programming voltage

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