WM8281ECSSLASHR datasheet(239/392 Pages) CIRRUS

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WM8281

Rev 4.0

239

PULSE WIDTH MODULATION (PWM) SIGNAL OUTPUT

GPn_FN = 08h, 09h.

The WM8281 incorporates two Pulse Width Modulation (PWM) signal generators which can be

enabled as GPIO outputs. 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.

The Pulse Width Modulation (PWM) outputs may be output directly on a GPIO pin by setting the

respective GPIO registers as described in “GPIO Control”.

See “Digital Core” for details of how to configure the PWM signal generators.

Note that the PWM output should always be disabled (PWMn_ENA=0, as described in Table 22)

whenever the system clock, SYSCLK, is disabled. Failure to do this may result in a persistent logic ‘1’

DC output from the PWM generator. See “Clocking and Sample Rates” for details of system clocking

and the associated control requirements.

HEADPHONE DETECTION STATUS OUTPUT

GPn_FN = 12h.

The WM8281 provides a headphone detection circuit on the HPDETL and HPDETR pins to measure

the impedance of an external load connected to the headphone outputs.

See “External Accessory

Detection

” for further details.

A logic signal from the headphone detection circuit may be output directly on a GPIO pin by setting

the respective GPIO registers as described in “GPIO Control”. This logic signal is set low when a

Headphone Detect measurement is triggered, and is set high when the Headphone Detect function

has completed. A rising edge indicates completion of a Headphone Detect measurement.

The headphone detection circuit is also an input to the Interrupt control circuit. An interrupt event is

triggered whenever a headphone detection measurement has completed. Note that the HPDET_EINT

flag is also asserted when the headphone detection is initiated. The associated interrupt bit is latched

once set; it can be polled at any time or u

sed to control the IRQ signal. See “Interrupts” for more

details of the Interrupt event handling.

MICROPHONE / ACCESSORY DETECTION STATUS OUTPUT

GPn_FN = 13h.

The WM8281 provides an impedance measurement circuit on the MICDETn pins to detect the

connection of a microphone or other external accessory.

See “External Accessory Detection” for

further details.

A logic signal from the microphone detect circuit may be output directly on a GPIO pin by setting the

respective GPIO registers as described in “GPIO Control”. This logic signal is set high for a pulse

duration of 31

s whenever an accessory insertion, removal or impedance change is detected.

The microphone detection circuit is also an input to the Interrupt control circuit. An interrupt event is

triggered whenever an accessory insertion, removal or impedance change is detected. The

associated interrupt bit is latched once set; it can be polled at any time or used to control the IRQ

signal. See “Interrupts” for more details of the Interrupt event handling.

HEADPHONE ENABLE STATUS OUTPUT

GPn_FN = 2Fh, 30h, 31h, 32h, 33h, 34h.

Whenever a headphone output path is enabled or disabled, a pop-suppression control sequence is

triggered. Status outputs indicating the progress of these sequences are provided. Note that this

provides

See “Output Signal Path” for details of the Output Enable functions.

A logic signal from the Headphone Enable control functions may be output directly on a GPIO pin by

setting the respective GPIO registers as described in “GPIO Control”. This logic signal is set high for a

short pulse duration (approx. 100ns) whenever the respective control sequence has completed. The

headphone control sequence status outputs are described in Table 92.

The Headphone Enable control sequences also provide inputs to the Interrupt control circuit. An

interrupt event is triggered on completion of the respective control sequence. The associated interrupt

bits are latched once set; they can be polled at any time or used to control the IRQ signal. See

“Interrupts” for more details of the Interrupt event handling.

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