18.3.3.10 Major Modes
The USART supports a set of different I2S formats as shown in
Table 18.9 USART I2S Modes on page 550
, but it is not limited to
these modes. MONO, JUSTIFY and DELAY in USARTn_I2SCTRL can be mixed and matched to create an appropriate format. MONO
enables mono mode, i.e. one data stream instead of two which is the default. JUSTIFY aligns data within a word on the I2S bus, either
left or right which can bee seen in figures
Figure 18.23 USART Left-Justified I2S Waveform on page 551
Right-Justified I2S Waveform on page 551
. Finally, DELAY specifies whether a new I2S word should be started directly on the edge of
the word-select signal, or one bit-period after the edge.
Table 18.9. USART I2S Modes
Mode
MONO
JUSTIFY
DELAY
CLKPOL
Regular I2S
0
0
1
0
Left-Justified
0
0
0
1
Right-Justified
0
1
0
1
Mono
1
0
0
0
The regular I2S waveform is shown in
Figure 18.21 USART Standard I2S Waveform on page 550
and
I2S Waveform (Reduced Accuracy) on page 550
. The first figure shows a waveform transmitted with full accuracy. The wordlength
can be configured to 32-bit, 16-bit or 8-bit using FORMAT in USARTn_I2SCTRL. In the second figure, I2S data is transmitted with re-
duced accuracy, i.e. the data transmitted has less bits than what is possible in the bus format.
Note that the msb of a word transmitted in regular I2S mode is delayed by one cycle with respect to word select
USn_CLK
USn_CS
(word select)
USn_TX/
USn_RX
MSB
Left channel
Right channel
Right channel
LSB
MSB
LSB
Figure 18.21. USART Standard I2S Waveform
USn_CLK
USn_CS
(word select)
USn_TX/
USn_RX
MSB
Left channel
Right channel
Right channel
LSB
MSB
Figure 18.22. USART Standard I2S Waveform (Reduced Accuracy)
A left-justified stream is shown in
Figure 18.23 USART Left-Justified I2S Waveform on page 551
. Note that the MSB comes directly
after the edge on the word-select signal in contradiction to the regular I2S waveform where it comes one bit-period after.
Reference Manual
USART - Universal Synchronous Asynchronous Receiver/Transmitter
silabs.com
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