WM8998 datasheet(87/307 Pages) WOLFSON

87 / 307 page

Production Data

WM8998

PD, October 2014, Rev 4.0

The WM8998 performs automatic checks to confirm that the SYSCLK frequency is high enough to

support the digital mixer paths. If an attempt is made to enable a PWM signal mixer path, and there

are insufficient SYSCLK cycles to support it, then the attempt will be unsuccessful. (Note that any

signal paths that are already active will not be affected under these circumstances.)

The Underclocked Error condition can be monitored using the GPIO and/or Interrupt functions. See

“General Purpose Input / Output” and “Interrupts” for further details.

The status bits in Registers R1600 to R2920 indicate the status of each of the digital mixers. If an

Underclocked Error condition occurs, then these bits provide readback of which mixer(s) have been

successfully enabled.

SAMPLE RATE CONTROL

The WM8998 supports multiple signal paths through the digital core. Stereo full-duplex sample rate

conversion is provided to allow digital audio to be routed between interfaces operating at different

sample rates and/or referenced to asynchronous clock domains.

Two independent clock domains are supported, referenced to SYSCLK and ASYNCCLK respectively,

as described in “Clocking and Sample Rates”. Every digital signal path must be synchronised either to

SYSCLK or to ASYNCCLK.

Up to five different sample rates may be in use at any time on the WM8998. Three of these sample

rates must be synchronised to SYSCLK; the remaining two, where required, must be synchronised to

ASYNCCLK.

Sample rate conversion is required when routing any audio path between digital functions that are

asynchronous and/or configured for different sample rates.

The Asynchronous Sample Rate Converter (ASRC) provides two signal paths between the SYSCLK

and ASYNCCLK domains. The ASRC is described later, and is illustrated in Figure 35.

There are two Isochronous Sample Rate Converters (ISRCs). These provide signal paths between

different sample rates on the SYSCLK domain, or between sample rates on the ASYNCCLK domain.

ISRC1 supports up to 4 signal paths; ISRC2 supports up to 2 signal paths. The ISRCs are described

later, and are illustrated in Figure 36.

The sample rate of different blocks within the WM8998 digital core are controlled as illustrated in

Figure 33 and Figure 34 - the *_RATE registers select the applicable sample rate for each respective

group of digital functions.

WM8998 Datasheet(PDF) 87 Page - Wolfson Microelectronics plc