I2S interface using LPC2138

Question

In my application, I am using LPC2138 controller and TI's TLV320DAC3100 DAC with built in amplifier to interface audio data.

To implement I2S interface using SPI, some extra hardware circuitry needed which I found from below link:

http://www.ti.com/lit/an/slaa449a/slaa449a.pdf

From above application note, I am able to get following hardware for SPI - I2S interface.

And 5 bit counter is implemented as follows:

My question is above note is specifically for MSP430F Texas controller and I need to interface with NXP LPC2138 controller.

In that case,Is this design logically correct for interfacing I2S on SPI bus? Or LPC associated hardware will differ for such implementation.

Thank you.

Answer 1

Oh, be careful with the NXP SPI controllers. I can only tell from experience with the LPC1768 but it seems that at least one of the two SPI peripherals are identical.

As said, there are two SPI controllers in your chip. I can't tell much about the first one (the ordinary SPI controller without FIFO). It may just work for your task, but - no FIFO, so very high CPU load.

The second one, called SPI1/SSP, is tricky because it demands that the chip-select line goes high between each transfer word for at least one clock cycle. This makes it impossible to transfer a continuous bit-stream without gaps. You will not be able to directly interface I2S in SPI mode.

You can however configure the SPI1/SSP in TI SSI mode. In this mode the chip-select line becomes a frame syncronization signal that stays low most of the time but pulses high on each least significant bit. The transfer will be continuous without single bit gaps so it interfaces nicely with your I2C codec.

You may be able to derive the I2S Word-Select signal from this using a single divider flip-flop. Deriving directly from clock like you suggested would work just as well.

I suggest that you take a look at figure 26 in the user manual UM10120: