STM8S datasheet(343/467 Pages) STMICROELECTRONICS

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RM0016

Universal asynchronous receiver transmitter (UART)

377

Figure 125. RX data setup/hold time

Note:

The function of UART_CK is different in Smartcard mode. Refer to Section 22.3.11:

Smartcard for more details.

22.3.10

Single wire half duplex communication

The UART can be configured to follow a single wire half duplex protocol. Single-wire half-

duplex mode is selected by setting the HDSEL bit in the UART_CR5 register. In this mode,

the following bits must be kept cleared:

•

LINEN and CLKEN bits in the UART_CR3 register

•

SCEN and IREN bits in the UART_CR5 register

Note:

This feature is only available in UART1 and UART4.

As soon as HDSEL is set:

•

UART_RX is no longer used

•

UART_TX is always released when no data is transmitted. Thus, it acts as a standard

I/O in idle or in reception. This means that the I/O must be configured so that UART_TX

is configured as floating input (or output high open-drain) when not driven by the UART.

Apart from this, the communications are similar to what is done in normal UART mode. The

conflicts on the line must be managed by the software (by the use of a centralized arbiter, for

instance). In particular, the transmission is never blocked by hardware and continue to occur

as soon as a data is written in the data register while the TEN bit is set.

22.3.11

Smartcard

Smartcard mode is selected by setting the SCEN bit in the UART_CR5 register. In

smartcard mode, the following bits must be kept cleared:

•

LINEN bit in the UART_CR3 register,

•

HDSEL and IREN bits in the UART_CR5 register.

Moreover, the CKEN bit may be set in order to provide a clock to the smartcard.

Note:

This feature is only available in UART1, UART2 and UART4.

The Smartcard interface is designed to support asynchronous protocol Smartcards as

defined in the ISO7816-3 standard. The UART should be configured as eight bits plus parity

and 1.5 stop bits. With Smartcard mode enabled (which can be done by setting the SCEN

bit in the UART_CR5) the UART can communication with an asynchronous Smartcard.

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