WM8351 datasheet(110/330 Pages) WOLFSON

110 / 330 page

WM8351

Production Data

PD, April 2012, Rev 4.5

110

14.3.6

RESET SIGNALS

The WM8351 provides an active-low reset output signal to the host processor on the open-drain /RST

pin. The /RST pin is asserted low in the OFF state. The status of the /RST pin in HIBERNATE state is

configurable using the RST_HIB_MODE bit.

In start-up, after all enabled power supplies reach 90% of their programmed output voltage, the /RST

output is held low for a programmable duration set by RSTB_TO. The /RST pin is then set high. The

/RST output is set low during the shutdown sequence.

In Configuration Mode 11 only, the “crystal detect” mode is enabled; this controls the /RST output

behaviour. In this mode, the WM8351 monitors the 32kHz crystal oscillator during start-up to verify

that the output frequency is valid. The /RST output is held low until this has been achieved.

An additional GPIO output, /RST can be generated, with the same functionality as the /RST pin. A

GPIO pin must be configured as /RST in order to output this signal (see Section 20).

The WM8351 can also generate a separate /MEMRST signal for other subsystems such as external

memory. This allows resetting some subsystems in the HIBERNATE state, while not resetting others.

The /MEMRST feature is provided via a GPIO pin (see Section 20). Note that /MEMRST is not a valid

control signal during the start-up as the GPIO pins are not configured at this time. The MEM_VALID

field provides an indication of whether the contents of the external memory (under control of

/MEMRST) are valid.

The /RST and /MEMRST signals can also be asserted under control of a manual reset input. A GPIO

pin (see Section 20) must be configured as /MR to enable this feature. Note that the /MR input has no

effect on the WM8351 circuits other than asserting /RST and /MEMRST.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R3 (03h)

System

Control 1

11:10

RSTB_TO

[1:0]

Time that the /RST pin and /MEMRST output

is held low after the chip reaches the active

state.

00 = 15ms

01 = 30ms

10 = 60ms

11 = 120ms

MEM_VALID

Indicates that the contents of external

memory are still valid.

This bit is cleared on startup and whenever

/MEMRST is asserted from the main state

machine. The system software should set

this bit once the external memory has been

set up.

Controlled in hibernate mode by

MEMRST_HIB_MODE

0 = External memory is not valid and needs

restoring.

1 = External memory is valid.

R5 (05h)

System

Hibernate

RST_HIB_M

ODE

/RST pin state in hibernate mode:

0 = Asserted (low)

1 = Not asserted (high)

MEMRST_H

IB_MODE

/MEMRST (Alternative GPIO function) pin

state in hibernate mode

0 = Asserted (low)

1 = Not asserted (high)

Table 60 Controlling Reset Signals

The WM8351 can be commanded to assert the /RST and /MEMRST signals by writing a logic ‘1’ to

the SYS_RST register bit. In this case, the /RST and /MEMRST outputs are asserted low for the

duration specified by RSTB_TO.

WM8351 Datasheet(PDF) 110 Page - Wolfson Microelectronics plc

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