EFM32WG Datasheet, PDF (457/834 Pages) List of Unclassifed Manufacturers – The EFM32WG Wonder Gecko is the ideal choice for demanding 8-, 16-, and 32-bit energy sensitive applications.

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The USn_CS output is active low by default, but its polarity can be changed with CSINV in
USARTn_CTRL. AUTOCS works regardless of which mode the USART is in, so this functionality can
also be used for automatic chip/slave select when in synchronous mode (e.g. SPI).
17.3.2.6.3 Two Data-links
Some limited devices only support half duplex communication even though two data links are available.
In this case software is responsible for making sure data is not transmitted when incoming data is
expected.
17.3.2.7 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 Figure 17.9 (p. 457) . The first element in the transmit buffer, i.e. element 0 in
Figure 17.9 (p. 457) is the first element written to the FIFO, or the least significant byte when writing
two bytes at a time using USARTn_TXDOUBLE.
Figure 17.9. USART Transmission of Large Frames
Peripheral Bus
TX buffer elem ent 1 0 1 2
Writ e CTRL
TX buffer elem ent 0 0 1 2 3 4 5 6 7
Writ e CTRL
Shift regist er
01234567 01 2
Writ e CTRL
As shown in Figure 17.9 (p. 457) , frame transmission control bits are taken from the second 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.
2013-05-08 - Wonder Gecko Family - d0233_Rev0.50
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