SAMD21 System Control Block (SCB) Overview

The System Control Block (SCB) is the programmer's model interface to the processor. It provides system implementation information and system control, including configuration, control, and reporting of system exceptions. The SCB registers are:

Address Name Type Reset value Description
0xE000ED00 CPUID RO 0x410CC601a CPUID Register
0xE000ED04 ICSR RWb 0x00000000 Interrupt Control and State Register
0xE000ED08 VTORc RW 0x00000000 Vector Table Offset Register
0xE000ED0C AIRCR RWb 0xFA050000 Application Interrupt and Reset Control Register
0xE000ED10 SCR RW 0x00000000 System Control Register
0xE000ED14 CCR RO 0x00000204 Configuration and Control Register
0xE000ED1C SHPR2 RW 0x00000000 System Handler Priority Register 2
0xE000ED20 SHPR3 RW 0x00000000 System Handler Priority Register 3

CPUID Register

The CPUID register contains the processor part number, version, and implementation information.

Interrupt Control and State Register

  • The ICSR provides:
    • A set-pending bit for the Non-Maskable Interrupt (NMI) exception.
    • Set-pending and clear-pending bits for the PendSV and SysTick exceptions
  • The ICSR indicates:
    • The exception number of the highest priority pending exception.

Vector Table Offset Register

If implemented, the VTOR indicates the offset of the vector table base address from memory address 0x00000000.

Application Interrupt and Reset Control Register

The AIRCR provides endian status for data accesses and reset control of the system.

System Control Register

The SCR controls features of entry to and exit from low power state.

Configuration and Control Register

The CCR is a read-only register and indicates some aspects of the behavior of the Arm® Cortex®-M0+ processor.

System Handler Priority Registers

The SHPR2-SHPR3 registers set the priority level (0 to 192) of the system exception handlers that have configurable priority.
SHPR2-SHPR3 are word accessible.

Ensure software uses aligned 32-bit word size transactions to access all the SCB registers.

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