HD6417660 RENESAS [Renesas Technology Corp], HD6417660 Datasheet - Page 68

• Manufacturer Part Number: HD6417660
• Description: Renesas 32-Bit RISC Microcomputer
• Manufacturer: RENESAS [Renesas Technology Corp]

2.1.2
This LSI supports two processing modes: user mode and privileged mode. These processing
modes can be determined by the processing mode bit (MD) in the status register (SR). If the MD
bit is cleared to 0, user mode is selected. If the MD bit is set to 1, privileged mode is selected.
The CPU automatically enters privileged mode by a transition to the reset state or exception
handling state. In privileged mode, any registers and resources in address spaces can be accessed.
For details on differences of registers and address spaces which can be accessed by the CPU in
each processing mode, refer to section 2.2, Memory Map and section 2.3, Register Descriptions.
Writing 0 to the MD bit in SR puts the CPU in user mode. In user mode, some of the registers,
including SR, and some of the address spaces cannot be accessed by the user program and system
control instructions cannot be executed. This function effectively protects the system resources
from the user program. To change the processing mode from user to privileged mode, a transition
to the exception handling state is required.*
Notes: 1. To call a service routine used in privileged mode from user mode, the LSI supports an
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2. When a transition from user mode to privileged mode occurs, the contents of SR and
Processing Modes (User Mode/Privileged Mode)
unconditional trap instruction (TRAPA).
PC are saved. A program execution in user mode can be resumed by restoring the
contents of SR and PC. To return from an exception handling program, the LSI
supports an RTE instruction.
(From any states)
Power-on reset
Manual reset
Exception handling state
exceptions
Multiple
Reset state
Figure 2.1 Processing State Transitions
routine starts
Exception
handling
1
*
Reset processing
2
routine starts
An exception
is accepted
An exception
is accepted
Program execution state
Power-down mode
SLEEP instruction