RM0440 Rev 4 1623/2126
RM0440 Universal synchronous/asynchronous receiver transmitter (USART/UART)
1733
Note: In master mode, the SCLK pin operates in conjunction with the TX pin. Thus, the clock is
provided only if the transmitter is enabled (TE=1) and data are being transmitted
(USART_TDR data register written). This means that it is not possible to receive
synchronous data without transmitting data.
Figure 542. USART example of synchronous master transmission
Figure 543. USART data clock timing diagram in synchronous master mode
(M bits =00)
MSv31158V1
USART
Synchronous device
(e.g. slave SPI)
RX
TX
Data out
Data in
Clock
SCLK
MSv34709V2
0 1 2 3 4 5 6 7
0 1 2 3 4 5 6 7
*
*
*
*
MSB
MSB
LSB
LSB
Start
Start Stop
Idle or preceding
transmission
Idle or next
transmission
*
*LBCL bit controls last data pulse
Capture strobe
Data on RX
(from slave)
Data on TX
(from master)
Clock (CPOL=1, CPHA=1)
Clock (CPOL=1, CPHA=0)
Clock (CPOL=0, CPHA=1)
Clock (CPOL=0, CPHA=0)
Stop
M bits = 00 (8 data bits)
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