ST STM8S Reference Manual

Universal asynchronous receiver transmitter (UART) RM0016
328/449 Doc ID 14587 Rev 8
Figure 124. 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.
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 and UART2.
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.
valid DATA bit
t
SETUP
t
HOLD
SCLK (capture strobe on SCLK
rising edge in this example)
Data on RX
(from slave)
t
SETUP
= t
HOLD
1/16 bit time = 1/16*f
SCLK

ST STM8S Specifications

General

Brand	ST
Model	STM8S
Category	Microcontrollers
Language	English