Can someone explain what is the difference between I2S interface and PCM interface. Does I2S interface only supports i2s format audio data and not PCM format audio data ?
Answer
PCM is a digital representation of an audio signal. It can be stored in memory or written on paper or whatever. An example of a 16-bit PCM audio sample might be something like 0x0152.
I2S is a electrical serial interface used to transmit PCM data from one device to another. The interface has a line used to delineate frames called the frame clock, a line for marking individual bits called the bit clock and 1 or more lines for the data. At the start of each frame clock a PCM sample is serialized bit by bit with a high voltage for a 1 and a zero voltage for a 0. The bit is held at that value for the entire duration of a bit clock and then it moves onto the next bit.
Here's some ascii art showing how an 8-bit sample 0x55 (01010101 binary), single channel might be transmitted. The frame clock runs at the sample rate, the bit clock at 8 times the sample rate and the data line contains the embedded data.
_______________ _
FCLK _| |_______________|
_ _ _ _ _ _ _ _ _
BCLK _| |_| |_| |_| |_| |_| |_| |_| |_|
___ ___ ___ ___
DATA ___0_| 1 |_0_| 1 | 0 | 1 |_0_| 1 |_
The wikipedia articles do a pretty good job of explaining.