PXD20RM Datasheet, PDF (1374/1628 Pages) Freescale Semiconductor, Inc – PXD20 Microcontroller

The 16-bit accumulator is incremented by the channel clock and generates the address to read the samples
from the FIFO. Only the upper 8 bits are used to select the address to the FIFO. The DDSF value provides
the increment of the 16-bit accumulator and so can be used to determine both the frequency of change of
sample as well as the sequence of samples:
• A value of 0x0100 will output sequential samples from the wavetable at a rate of one per DDS
clock cycle
• A value of 0x0200 will output every second sample from the wavetable at a rate of one per DDS
clock cycle
• A value of 0x0001 will output sequential samples from the wavetable at a rate of one every 256
DDS clock cycles
• A value of 0x00C0 will output the sequence sample 0, sample 1, sample 2, sample 3, sample 3,
sample 4, sample 5, sample 6, sample 7, sample 7 and so on at the DDS clock rate
Since only the upper 8 bits of the accumulator are used to address the wavetable, the sample rate is:
F_ddsout
=
F_{----d---d--s-c--l--k  DDSF}
2¹⁶
The repetition frequency of the wavetable contents is given by:
fwave = Fddsclk/DDSF
Eqn. 39-1
39.7.5.2 ASR Envelope Controller
The SGM provides a simple, configurable ASR envelope, which is a simplified ADSR envelope. See
Figure . The envelope controller controls the volume of each sample output from the DDS Controller.
39.7.5.3 Sample Format Converter
In Wave mode, linear mono PCM data coded in 8-bit, 12-bit and 16-bit are supported.
The Sample Format Converter (SFC) converts data coded in 8 or 12 bit into 16-bit linear PCM data
(represented by two’s complement).
39.7.5.4 Volume Control
The Volume Controller is used to adjust the volume of the sound. For each channel, the volume can be
controlled individually. A fixed-point multiplier is applied to each channel to compute the required sample
value for the resampler and mixer.
39-50
PXD20 Microcontroller Reference Manual, Rev. 1
Preliminary—Subject to Change Without Notice
Freescale Semiconductor