21.3.1 SFRBU Power Switch BU Control Register
| Name: | SFRBU_PSWBUCTRL |
| Offset: | 0x00 |
| Reset: | 0x00000009 |
| Property: | Read/Write |
| Bit | 31 | 30 | 29 | 28 | 27 | 26 | 25 | 24 | |
| KEY_PSW_MODE[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 | |
| KEY_PSW_MODE[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 | |
| KEY_PSW_MODE[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 | SMCTRL | SSWCTRL | SCTRL | ||||||
| Access | R | R/W | R/W | R/W | |||||
| Reset | 1 | 0 | 0 | 1 |
Bits 31:8 – KEY_PSW_MODE[23:0] Specific value mandatory to allow writing of other register bits (Write-only)
This field is a security key to prevent power switch changes due to software error or malicious code.
| Value | Description |
|---|---|
| 0x4BD20C |
SFRBU_PSWBUCTRL register write possible. |
| Other values |
SFRBU_PSWBUCTRL register write impossible. |
Bit 3 – 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 | Description |
|---|---|
| 0 | LDO BU Supply source is VDDBU. |
| 1 | LDO BU Supply source is VDDANA. |
Bit 2 – SMCTRL Allow Power Switch BU Control by Security Module Autobackup (Hardware)
Enables automatic selection of the VDDBU source when the security module enters Backup mode.
This automatic supply source switching is independent from the SCTRL and SSWCTRL bits.
| Value | Description |
|---|---|
| 0 | Reset value. No automatic supply source switching from security module. |
| 1 | Automatic supply source switching from security module activated. |
Bit 1 – SSWCTRL Power Switch BU Source Selection
Has an action only if SCTRL bit value is “1”.
| Value | Description |
|---|---|
| 0 | Reset value. LDO Supply source is VDDBU. |
| 1 | LDO Supply source is VDDANA. |
Bit 0 – SCTRL Power Switch BU Software Control
Used to control the Power Switch BU state by software in addition to the SSWCTRL bit.
| Value | Description |
|---|---|
| 0 | Power Switch BU is controlled by hardware (SSWCTRL bit has no action). |
| 1 | Reset value. Power Switch BU is controlled by software (SSWCTRL bit has an action). |