using SPI with an LPCXpresso 54102 digital microphone

[lpcware]

Content originally posted in LPCWare by sbishop77 on Tue Nov 03 19:24:14 MST 2015
I am trying to figure out how to use the DMIC marked "M4" on the sensor shield of the LPCX54102, via SPI.  (This is also my first time using SPI.)

It looks like it's necessary to short jumpers JP2 and JP5, which I have done.  But I am confused regarding the SPI1_SCK and SPI1_MOSI traces.  (I'm looking at page three of the shield schematic.)  It seems like the LPC54102 would have to drive the clock (SPI1_SCK) as if it were the master and read the data (SPI1_MOSI) as if it were the slave.  And what about a slave-select pin?  How is this supposed to work?

[lpcware]

Content originally posted in LPCWare by bavarian on Tue Nov 17 01:40:08 MST 2015
Well, looking at it with the SPI in mind for connecting a DMIC, you could think of a design mistake. But it's not so simple ;-)

The LPC54102 contains a little sub-processor (the I/O handler which we documented for the LPC11U3x), which can do the DMIC data sampling and the filtering from PDM to PCM data. The input/output definitions of the shield board fit to this I/O handler peripheral.

As this sub-processor is a little bit tricky to program, we are working on a library component for the LPC54102 which can be used in generic software projects for providing the DMIC functionality. Using SPI is of course a valid option as well, but using the I/O handler for that is much smarter and more energy efficient.

Regards,
NXP Support Team.

[lpcware]

Content originally posted in LPCWare by sbishop77 on Wed Nov 04 08:11:42 MST 2015
Thank you, mysepp.  After reviewing that page, I am almost certain that there's a simple issue with the design of the shield, where the microphone should have been connected to the MISO pin of the MCU instead of the MOSI pin.

[lpcware]

Content originally posted in LPCWare by mysepp on Tue Nov 03 23:09:50 MST 2015
Not related to NXP controller, but SPI in general:
https://en.wikipedia.org/wiki/Serial_Peripheral_Interface_Bus