PM0056 datasheet(15/156 Pages) STMICROELECTRONICS

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PM0056

The Cortex-M3 processor

General-purpose registers

R0-R12 are 32-bit general-purpose registers for data operations.

Stack pointer

The Stack Pointer (SP) is register R13. In Thread mode, bit[1] of the CONTROL register

indicates the stack pointer to use:

•

0 = Main Stack Pointer (MSP). This is the reset value.

•

1 = Process Stack Pointer (PSP).

On reset, the processor loads the MSP with the value from address 0x00000000.

Link register

The Link Register (LR) is register R14. It stores the return information for subroutines,

function calls, and exceptions. On reset, the processor loads the LR value 0xFFFFFFFF.

Program counter

The Program Counter (PC) is register R15. It contains the current program address. Bit[0] is

always 0 because instruction fetches must be halfword aligned. On reset, the processor

loads the PC with the value of the reset vector, which is at address 0x00000004.

read-write Either

0xFFFFFFFF

Link register on page 15

read-write Either

See description Program counter on page 15

PSR

read-write Privileged

0x01000000

Program status register on page 16

ASPR

read-write Either

0x00000000

Application program status register on

page 17

IPSR

read-only

Privileged

0x00000000

Interrupt program status register on

page 18

EPSR

read-only

Privileged

0x01000000

Execution program status register on

page 19

PRIMASK

read-write Privileged

0x00000000

Priority mask register on page 20

FAULTMASK

read-write Privileged

0x00000000

Fault mask register on page 20

BASEPRI

read-write Privileged

0x00000000

Base priority mask register on page 21

CONTROL

read-write Privileged

0x00000000

CONTROL register on page 21

1. Describes access type during program execution in thread mode and Handler mode. Debug access can

differ.

2. An entry of Either means privileged and unprivileged software can access the register.

Table 2. Core register set summary (continued)

Name

Type(1)

Required

privilege(2)

Reset

value

Description

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