Word Width vs clock number per word in SAI

[sergeysokolov]

Hi,

Is clock number per word in SAI equal to Word N Width (I2S_TCR5[WNW]) or W0W(I2S_TCR5[W0W])?

Or clock number per word is always 32? as one might think by reading the following I2S_TCR5[FBT]

...The value written must be less than or equal to 31-word width when configured for LSB First.

Thank you.

[carlos_neri]

The very first word of each frame equals to W0W, the remaining words on a frame equals to WNW. That being said, if you're trying to implement I2S, you should use WNW = W0W to match what you need, usually 32-bit (WNW = W0W = 0x1F).

[sergeysokolov]

Yes, I understand this, but when I read FBT definition, for instance

"..The value written must be greater than or equal to the word width when configured for MSB First."

How the value might be greater than word width?

[carlos_neri]

the value might be greater than the word with when is configured to be less than 32-bit. Let's say you want 24-bit word width and configure it as it. You can write the data register with 32-bit word with your 24-bit data right justified, then, you'll need to configure FBT to start sending data from bit 23, or if your data is left justified, then, you'll need to configure FBT to start sending data from bit 31 (assuming MSB is transmitted first).