Motorola DSP56012 User Manual

For proper operation of the DAX, the DSP core clock frequency must be at 
least five times higher than the DAX bit shift clock frequency (64 

×

 Fs).

The DAX state machine generates a set of sequencing signals used in the DAX.

To initiate the DAX operation, follow this procedure: 

1. Write the audio data in the XADRA/XADRB registers

2. Write the non-audio data and transmit mode to the corresponding bits in the 

XCTR register; ensure that the XEN bit remains cleared

3. Set the XEN bit in the XCTR; transmission begins

When the XIEN bit is set and the DAX is active, a Transmit Audio Data register 
Empty interrupt (XADE = 1) is generated once at the beginning of every frame 
transmission. Typically, within an XADE interrupt, one frame of audio data to be 
transmitted in the next frame is stored in the XADRA and the XADRB by two 
consecutive MOVEP instructions within a fast interrupt routine. This clears the 
XADE bit in the XSTR.

An interrupt with the XBLK vector indicates the end of a block transmission and can 
require some computation to provide the next non-audio data structures that are to 
be transmitted within the next block. Within the routine, the next audio data can be 
stored in the XADRA/XADRB registers, and the next non-audio data can also be 
stored in the XCTR.