WM8998 Datasheet, PDF (85/307 Pages) Wolfson Microelectronics plc – High Performance Audio Hub CODEC

Production Data
WM8998
PWM GENERATOR
The WM8998 incorporates two Pulse Width Modulation (PWM) signal generators as illustrated in
Figure 32. The duty cycle of each PWM signal can be modulated by an audio source, or can be set to
a fixed value using a control register setting.
A 4-input mixer is associated with each PWM generator. The 4 input sources are selectable in each
case, and independent volume control is provided for each path.
The PWM signal generators can be output directly on a GPIO pin. See “General Purpose Input /
Output” to configure a GPIO pin for this function.
Note that the PWM signal generators cannot be selected as input to the digital mixers or signal
processing functions within the WM8998 digital core.
When PWMn_OVD = 0, the PWM duty cycle is controlled by the respective digital audio mixer.
When PWMn_OVD = 1, the PWM duty cycle is set by PWMn_LVL.
The PWM sample rate and clocking frequency are selected using PWM_RATE and PWM_CLK_SEL.
PWM1MIX_SRC1
PWM1MIX_VOL1
PWM1MIX_SRC2
PWM1MIX_VOL2
+
PWM1MIX_SRC3
PWM1MIX_VOL3
PWM1MIX_SRC4
PWM1MIX_VOL4
PWM2MIX_SRC1
PWM2MIX_VOL1
PWM2MIX_SRC2
PWM2MIX_VOL2
+
PWM2MIX_SRC3
PWM2MIX_VOL3
PWM2MIX_SRC4
PWM2MIX_VOL4
PWM1
PWM1_ENA
PWM1_OVD
PWM1_LVL
GPIO
(GPn = 08h)
PWM_RATE
PWM_CLK_SEL
PWM2
PWM2_ENA
PWM2_OVD
PWM2_LVL
GPIO
(GPn = 09h)
Figure 32 Digital Core Pulse Width Modulation (PWM) Generator
The PWM1 and PWM2 mixer control registers (see Figure 32) are located at register addresses
R1600 (640h) through to R1615 (64Fh).
The full list of digital mixer control registers is provided in the “Register Map” section (Register R1600
through to R2920). Generic register definitions are provided in Table 7.
The *_SRCn registers select the input source(s) for the respective mixers. Note that the selected input
source(s) must be configured for the same sample rate as the mixer to which they are connected.
Sample rate conversion functions are available to support flexible interconnectivity - see
“Asynchronous Sample Rate Converter (ASRC)” and “Isochronous Sample Rate Converter (ISRC)”.
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PD, October 2014, Rev 4.0
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