32.3.1 SFRBU Power Switch BU Control Register

The backup power switch selects the primary power source for the backup regulator (either VBAT or VDDIN33).

Name:	SFRBU_PSWBU
Offset:	0x00
Reset:	0x00000001
Property:	Read/Write


Bit	31	30	29	28	27	26	25	24
	PSWKEY[23:16]
Access	W	W	W	W	W	W	W	W
Reset	0	0	0	0	0	0	0	0


Bit	23	22	21	20	19	18	17	16
	PSWKEY[15:8]
Access	W	W	W	W	W	W	W	W
Reset	0	0	0	0	0	0	0	0


Bit	15	14	13	12	11	10	9	8
	PSWKEY[7:0]
Access	W	W	W	W	W	W	W	W
Reset	0	0	0	0	0	0	0	0


Bit	7	6	5	4	3	2	1	0
						STATE	SOFTSWITCH	CTRL
Access						R	R/W	R/W
Reset						0	0	1

Bits 31:8 – PSWKEY[23:0] Specific Value Mandatory to Allow Writing of Other Register Bits (Write-only)

PSWKEY is a security key preventing power switch changes due to software error or malicious code.

Value	Name	Description
0x4BD20C	PASSWD	Writing any other value in this field aborts the write operation in the SFRBU_PSWBU register. Always reads as 0.

Value

Name

Description

0x4BD20C

PASSWD

Writing any other value in this field aborts the write operation in the SFRBU_PSWBU register.

Always reads as 0.

Bit 2 – STATE Power Switch BU State (Read-only)

Reflects the power switch BU supply source selection in real time. After a switching request, the user must wait for the analog cell switching time to have an updated status (see the section Electrical Characteristics).

Value	Name	Description
0	VBAT	LDO Supply source is VBAT.
1	VDDIN33	LDO Supply source is VDDIN33.

Bit 1 – SOFTSWITCH Power Switch BU Source Selection

Has an action only if CTRL is set to ‘1’.

Value	Name	Description
0	VBAT	LDO Supply source is VBAT.
1	VDDIN33	LDO Supply source is VDDIN33.

Bit 0 – CTRL Power Switch BU Control

Used to control the Power Switch BU state by software.

Value	Name	Description
0	HARD	Power Switch BU is controlled by hardware (SOFTSWITCH bit has no action).
1	SOFT	Power Switch BU is controlled by software (SOFTSWITCH bit has an action).