WM8321 datasheet(130/253 Pages) WOLFSON

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WM8321

Production Data

PD, February 2012, Rev 4.0

130

24.2 HARDWARE RESET

A Hardware Reset is triggered when an external source pulls the RESET

¯¯¯¯¯¯ pin low. Under this

condition, the WM8321 transitions to the OFF state. The contents of the Register map are cleared to

default values, except for the RTC and software scratch registers, which are maintained. The

WM8321 will then automatically schedule an ON state transition to resume normal operation.

If the external source continues to pull the RESET

¯¯¯¯¯¯ pin low, then the WM8321 cannot fully complete

the ON state transition following the Hardware Reset. In this case, the WM8321 will mask the external

reset for up to 32 seconds. If the RESET

¯¯¯¯¯¯ pin is released (ie. it returns to logic ‘1’) during this time,

then the ON state transition is completed and the Hardware Reset input is valid again from this point.

If the RESET

¯¯¯¯¯¯ pin is not released, then the WM8321 will force an OFF condition on expiry of the 32

seconds timeout. Recovery from this forced OFF condition cannot occur until the external reset

condition is de-asserted, followed by a valid ON event. If an ON event occurs before the external

reset is de-asserted, then start-up will be attempted, but the transition will be unsuccessful, causing a

return to the OFF state.

It is possible to mask the RESET

¯¯¯¯¯¯ pin input in the SLEEP state by setting the RST_SLP_MSK register

bit as described in Section 11.7.

24.3 SOFTWARE RESET

A Software Reset is triggered by writing to Register 0000h, as described in Section 12.5. In this event,

the WM8321 asserts the RESET

¯¯¯¯¯¯ pin and transitions to the OFF state. If the Reset occurred in the ON

state, then the WM8321 will automatically return to the ON state following the Reset.

The SWRST_DLY register field determines whether a time delay is applied between the Software

Reset command and the resultant shutdown and start-up sequences. When the SWRST_DLY bit is

set, the programmable time delay PWRSTATE_DLY is applied before commencing the shutdown

sequence.

The timing of the Software Reset is illustrated in Figure 25. See Section 11.3 for a definition of the

PWRSTATE_DLY register.

The SW_RESET_CFG register field determines if the Register Map is reset under a Software Reset

condition.

Note that the SW_RESET_CFG control register is locked by the WM8321 User Key. This register can

only be changed by writing the appropriate code to the Security register, as described in Section 12.4.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R16387

(4003h)

Power State

SWRST_DLY

Software Reset Delay

0 = No delay

1 = Software Reset is delayed by

PWRSTATE_DLY following the Software

Reset command

R16390

(4006h)

Reset

Control

SW_RESET_C

Software Reset Configuration.

Selects whether the register map is reset to

default values when Software Reset occurs.

0 = All registers except RTC and Software

Scratch registers are reset by Software

Reset

1 = Register Map is not affected by Software

Reset

Protected by user key

Table 77 Software Reset Configuration

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