Sound_Bytes ($F27D)

Sound_Bytes_x ($F284)

This routine copies a block of sound information into the sound chip buffer (at $C800-$C80E) and into the registers on the music chip. The format for the block of sound data is as follows:

(register number), (music data),
(register number), (music data),
. .
. .
0xFF

As long as the register number is >= 0, then the music data will be copied; however, as soon as a register number < 0 is encountered, the copy will stop.

ENTRY:

DP = $D0

U-reg = pointer to the block of sound data

EXIT:

D-reg, X-reg, U-reg trashed

Source