PCM1774: Register 81 and RFM bitfield are not documented

Hi Bob,

I am not sure why this is in the data sheet, but I do not have any information on what RFM is, but register 81 is not shown in the data sheet, therefore I do not believe that it is necessary for the operation of the part. Are you having any issues with the part?

Justin

There are no obvious problems; I just want to ensure that I am programming the device optimally for best performance.

I do have another question about the programming of register 84 (0x54).  We are using the PCM1774 in I2S Slave Mode and are providing 24 BCK pulses per sample (i.e. 48 * fs).  Our PCM1774 configuration (i.e. list of register writes) was developed by a former employee and programs register 84 to 0x02 (i.e. MSTR = 0, reserved bit 1 = 1, and BIT0 = 0).  The datasheet specifies that the BIT0 default value is 1 (corresponding to 16-bit data length), and the BIT0 value of 0 is reserved.

I don't have any supporting documentation to know if writing register 84 to 0x02 instead of 0x01 was previously recommended by TI, or just a mistake.  Would there be any reason to set register 84 to 0x02?

Thanks,

Bob Giaraffa

Hi Bob,

I recommend that register 81 should be left at default values, as well as B1 of register 84 be left at its default value.

Justin