Renesas SH7781 - Manual (Page 56)

2. Programming Model
Rev.1.00 Jan. 10, 2008 Page 26 of 1658
REJ09B0261-0100
2.2 Register Descriptions
2.2.1 Privileged Mode and Banks
(1) Processing Modes
This LSI has two processing modes, user mode and privileged mode. This LSI normally operates
in user mode, and switches to privileged mode when an exception occurs or an interrupt is
accepted. There are four kinds of registers—general registers, system registers, control registers,
and floating-point registers—and the registers that can be accessed differ in the two processing
modes.
(2) General Registers
There are 16 general registers, designated R0 to R15. General registers R0 to R7 are banked
registers which are switched by a processing mode change.
• Privileged mode
In privileged mode, the register bank bit (RB) in the status register (SR) defines which banked
register set is accessed as general registers, and which set is accessed only through the load
control register (LDC) and store control register (STC) instructions.
When the RB bit is 1 (that is, when bank 1 is selected), the 16 registers comprising bank 1
general registers R0_BANK1 to R7_BANK1 and non-banked general registers R8 to R15 can
be accessed as general registers R0 to R15. In this case, the eight registers comprising bank 0
general registers R0_BANK0 to R7_BANK0 are accessed by the LDC/STC instructions.
When the RB bit is 0 (that is, when bank 0 is selected), the 16 registers comprising bank 0
general registers R0_BANK0 to R7_BANK0 and non-banked general registers R8 to R15 can
be accessed as general registers R0 to R15. In this case, the eight registers comprising bank 1
general registers R0_BANK1 to R7_BANK1 are accessed by the LDC/STC instructions.
• User mode
In user mode, the 16 registers comprising bank 0 general registers R0_BANK0 to R7_BANK0
and non-banked general registers R8 to R15 can be accessed as general registers R0 to R15.
The eight registers comprising bank 1 general registers R0_BANK1 to R7_BANK1 cannot be
accessed.
(3) Control Registers
Control registers comprise the global base register (GBR) and status register (SR), which can be
accessed in both processing modes, and the saved status register (SSR), saved program counter
(SPC), vector base register (VBR), saved general register 15 (SGR), and debug base register