Product Specs

44 I
2
S — Inter-IC sound interface
Page
449
When using I
2
S format, the first bit in a half-frame (containing one left or right sample) gets sampled on the
second rising edge of the SCK after a LRCK edge. When using Aligned mode, the first bit in a half-frame
gets sampled on the first rising edge of SCK following a LRCK edge.
For data being received on SDIN the sample value can be either right or left-aligned inside a half-frame, as
specified in CONFIG.ALIGN on page 458. CONFIG.ALIGN on page 458 affects only the decoding of
the incoming samples (SDIN), while the outgoing samples (SDOUT) are always left-aligned (or justified).
When using left-alignment, each half-frame starts with the MSB of the sample value (both for data being sent
on SDOUT and received on SDIN).
When using right-alignment, each half-frame of data being received on SDIN ends with the LSB of the
sample value, while each half-frame of data being sent on SDOUT starts with the MSB of the sample value
(same as for left-alignment).
In Master mode, the size of a half-frame (in number of SCK periods) equals the sample width (in number of
bits), and in this case the alignment setting does not care as each half-frame in any case will start with the
MSB and end with the LSB of the sample value.
In slave mode, however, the sample width does not need to equal the frame size. This means you might
have extra or fewer SCK pulses per half-frame than what the sample width specified in CONFIG.SWIDTH
requires.
In the case where we use left-alignment and the number of SCK pulses per half-frame is higher than the
sample width, the following will apply:
• For data received on SDIN, all bits after the LSB of the sample value will be discarded.
• For data sent on SDOUT, all bits after the LSB of the sample value will be 0.
In the case where we use left-alignment and the number of SCK pulses per frame is lower than the sample
width, the following will apply:
• Data sent and received on SDOUT and SDIN will be truncated with the LSBs being removed first.
In the case where we use right-alignment and the number of SCK pulses per frame is higher than the
sample width, the following will apply:
• For data received on SDIN, all bits before the MSB of the sample value will be discarded.
• For data sent on SDOUT, all bits after the LSB of the sample value will be 0 (same behavior as for left-
alignment).
In the case where we use right-alignment and the number of SCK pulses per frame is lower than the
sample width, the following will apply:
• Data received on SDIN will be sign-extended to "sample width" number of bits before being written to
memory.
• Data sent on SDOUT will be truncated with the LSBs being removed first (same behavior as for left-
alignment).
LRCK
SCK
SDIN or SDOUT
frame
left
right
left
Figure 132: I
2
S format. CONFIG.SWIDTH equalling half-frame size.
LRCK
SCK
SDATA
Figure 133: Aligned format. CONFIG.SWIDTH equalling half-frame size.
frame
left
left
right