4.13.3.1 SFRBU VDDBU Power Switch 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 3130292827262524 
 PSWKEY[23:16] 
Access WWWWWWWW 
Reset 00000000 
Bit 2322212019181716 
 PSWKEY[15:8] 
Access WWWWWWWW 
Reset 00000000 
Bit 15141312111098 
 PSWKEY[7:0] 
Access WWWWWWWW 
Reset 00000000 
Bit 76543210 
      STATESOFTSWITCHCTRL 
Access RR/WR/W 
Reset 001 

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.

ValueNameDescription
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 VDDBU Power Switch State (Read-only)

Reflects the VDDBU power switch supply source selection in real time. After a switching request, the user must wait for one MD_SLCK cycle to get an updated status.

ValueNameDescription
0 VBAT The VDDBU supply source is VBAT.
1 VDDIN33 The VDDBU supply source is VDDIN33.

Bit 1 – SOFTSWITCH VDDBU Power Switch Source Selection

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

ValueNameDescription
0 VBAT The VDDBU supply source is VBAT.
1 VDDIN33 The VDDBU supply source is VDDIN33.

Bit 0 – CTRL VDDBU Power Switch Control

Used to control the VDDBU Power Switch state by software..

ValueNameDescription
0 HARD The VDDBU power switch is controlled by hardware (the SOFTSWITCH bit has no action).
1 SOFT The VDDBU power switch is controlled by software (the SOFTSWITCH bit has an action).