Help: Interface with a PCM3500 voice codec

[FoxtrotMike]

Hi:

·I want to interface a PCM3500 voice codec with a PIC, in order to store digitized voice in a PC via the UART, and then play it back. This chip has on board 16 bits ADC and DAC, and a synchronous serial port with 4 lines: FS (frame sync), BCK (bit clock), DIN (serial data in), DOUT (serial data out).

·The problem is that a frame is 16 bits long, containing a full conversion result, and i don't know how to make the PIC read that. I thought of using the SPI port, but the SPI_WRITE and SPI_READ functions are intended to work with 8 bits registers, so it seems it's not possible to read or write 16 bits at once.

·About the timing, it depends on the sampling frequency; each frame lasts Tf = 1/Fs, and each bit lasts Tb = 1/(16*Fs). For example, at 8 [kHz], each frame last 125 [us], and each bit lasts 7.8 [us].

·This chip can be be both slave and master; the frame sync pin can be used as an input (slave) or input (master). A frame sync signal is a pulse with a duration of Tb, and it repeats every Tf.

·I guess it's possible to do the transmission by bit banging, and the reception by using an external interrupt, but it seems a little messy, so if there's a better way to do it, please let me know about it.

·By the way, i'm using a PIC18F252 with a 20 [MHz] xtal. If anyone can give me a hand, i'll be grateful.

Best regards,
Fernando

[ECACE]

Not sure which version you are using, but in PCWH latest revisions, there is spi_xfer(), which allows you to define the number of bits to transfer. This would be a software SPI port, which is slower and would tie up the application while it is operating, but is a way you could do it. Otherwise, you may have to roll out your own SPI read/write functions.
Best of luck.
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