Silicon Laboratories EFR32xG14 Wireless Gecko Reference Manual page 542

18.3.2.19 Large Frames
As each frame in the transmit and receive buffers holds a maximum of 9 bits, both the elements in the buffers are combined when
working with USART-frames of 10 or more data bits.
To transmit such a frame, at least two elements must be available in the transmit buffer. If only one element is available, the USART will
wait for the second element before transmitting the combined frame. Both the elements making up the frame are consumed when
transmitting such a frame.
When using large frames, the 9th bits in the buffers are unused. For an 11 bit frame, the 8 least significant bits are thus taken from the
first element in the buffer, and the 3 remaining bits are taken from the second element as shown in
of Large Frames on page 542. The first element in the transmit buffer, i.e. element 0 in
Frames on page 542 is the first element written to the FIFO, or the least significant byte when writing two bytes at a time using
USARTn_TXDOUBLE.
As shown in Figure 18.11 USART Transmission of Large Frames on page
ond element in FIFO.
The two buffer elements can be written at the same time using the USARTn_TXDOUBLE or USARTn_TXDOUBLEX register. The
TXDATAX0 bitfield then refers to buffer element 0, and TXDATAX1 refers to buffer element 1.
Figure 18.12 USART Transmission of Large Frames, MSBF on page 542
frame is transmitted with MSBF set. If MSBF is set and the frame is smaller than 10 bits, only the contents of transmit buffer 0 will be
transmitted.
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USART - Universal Synchronous Asynchronous Receiver/Transmitter
TX buffer element 1 0 1
TX buffer element 0 0 1
Shift register
0 1 2 3 4 5 6 7
Figure 18.11. USART Transmission of Large Frames
TX buffer element 1
TX buffer element 0
2 1 0 7 6 5
Figure 18.12. USART Transmission of Large Frames, MSBF
Peripheral Bus
2
2 3 4 5 6 7
0 1 2
542, frame transmission control bits are taken from the sec-
Peripheral Bus
0 1 2
0 1 2 3 4 5 6 7
Shift register
4 3 2 1 0
illustrates the order of the transmitted bits when an 11 bit
Reference Manual
Figure 18.11 USART Transmission
Figure 18.11 USART Transmission of Large
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