ISD91200 Series Technical Reference Manual
Release Date: Sep 16, 2019
- 399 -
Revision 2.4
7.3.4.1
DPWM switch frequecy
HCLK
DPWM_CLK=
HCLK/DPWMDIV
Switch frequency
49.152MHz
24.576MHz
614.4KHz
12.288MHz
307.2KHz
8.192MHz
204.8KHz
6.144MHz
153.6KHz
7.3.4.2
DPWM Clock Generator
0
1
CLK12M
DPWMCKSEL(CLK_CLKSEL1[5:4])
DPWMCKEN(CLK_APBCLK0[13])
DPWM_CLK
1/(D 1)
DPWMDIV
(CLK_CLKDIV0[15:12])
HCLK
Note: Before clock switching, both the pre-selected and newly
selected clock sources must be turned on and stable.
7.3.4.3
Determining Sample Rate
The sample rate at which the DPWM block consumes audio data is given by:
Fs = DWPM_CLK ÷ ZOHDIV ÷64 ÷BIQ_CTL.DPWMPUSR
Where HCLK is the master CPU clock rate and DPWM_ZOHDIV is the divider control register. A table
of common audio sample rates is provided below.
Table 7-1 DPWM Sample Rates for Various HCLK
DPWM_CLK = 24.576MHz
Fs
(sample rate)
ZOHDIV (clock divider)
0x40070010
BIQ Enable
BIQ_CTL.DPWMPUSR
DPWM OSR
48KHz
8
off
1x
64
4
on
2x
128
2
on
4x
256
32KHz
12
off
1x
64
6
on
2x
128
4
on
3x
192
3
on
4x
256