Motorola DSP56012 Manuel D’Utilisation

The DAX consists of:

• Audio Data Register A and Audio Data Register B (XADRA and XADRB), one 

for each channel 

• Audio Data Buffer (XADBUF)

• Non-Audio Data Buffer (XNADBUF)

• Audio and non-audio Data Shift Register (XADSR)

• Control Register (XCTR)

• Status Register (XSTR)

• Parity Generator (PRTYG)

• Preamble generator

• Biphase encoder

• Clock multiplexer

• Control state machine

One frame of audio data and non-audio data (stored in XADRA/XADRB and XCTR, 
respectively) is transferred to the XADSR (for Channel A) and to the 
XADBUF/XNADBUF registers (for Channel B) at the beginning of a frame 
transmission. This is called an “upload.” At this time the DAX Audio Data register 
Empty (XADE) flag is set, and, if DAX interrupt is enabled, an interrupt request is 
sent to the DSP core. The interrupt handling routine then stores the next frame of 
audio data in the XADRA/XADRB and the non-audio data bits in the XCTR.

At the beginning of a frame transmission, one of the 8-bit Channel A preambles 
(Z-preamble for the first sub-frame in a block, or X-preamble otherwise) is generated 
in the preamble generator, and then shifted out to the ADO pin in the first eight time 
slots. The preamble is generated in biphase mark format. The twenty-four audio and 
three non-audio data bits in the XADSR are shifted out to the biphase encoder, which 
shifts them out through the ADO pin in the biphase mark format in the next fifty-four 
time slots. The parity generator calculates an even parity over the 27 bits of audio and 
non-audio data, and then outputs the result through the biphase encoder to the ADO 
pin at the last two time slots. This is the end of the first (Channel A) sub-frame 
transmission.