Section 2 CPU
2.1
Register Configuration
2.1.1
Privileged Mode and Banks
Processor Modes: There are two processor modes: user mode and privileged mode. The
SH7709S normally operates in user mode, and enters privileged mode when an exception occurs
or an interrupt is accepted. There are three kinds of registers—general registers, system registers,
and control registers—and the registers that can be accessed differ in the two processor modes.
General Registers: There are 16 general registers, designated R0 to R15. General registers R0 to
R7 are banked registers which are switched by a processor mode change. 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, the 16 registers comprising BANK1 general registers R0_BANK1–
R7_BANK1 and non-banked general registers R8–R15 function as the general register set, with
the 8 registers comprising BANK0 general registers R0_BANK0–R7_BANK0 accessed only by
the LDC/STC instructions.
When the RB bit is 0, BANK0 general registers R0_BANK0–R7_BANK0 and nonbanked general
registers R8–R15 function as the general register set, with BANK1 general registers R0_BANK1–
R7_BANK1 accessed only by the LDC/STC instructions. In user mode, the 16 registers
comprising bank 0 general registers R0_BANK0–R7_BANK0 and non-banked registers R8–R15
can be accessed as general registers R0–R15, and bank 1 general registers R0_BANK1–
R7_BANK1 cannot be accessed.
Control Registers: Control registers comprise the global base register (GBR) and status register
(SR) which can be accessed in both processor modes, and the saved status register (SSR), saved
program counter (SPC), and vector base register (VBR) which can only be accessed in privileged
mode. Some bits of the status register (such as the RB bit) can only be accessed in privileged
mode.
System Registers: System registers comprise the multiply and accumulate registers
(MACL/MACH), the procedure register (PR), and the program counter (PC). Access to these
registers does not depend on the processor mode.
The register configuration in each mode is shown in figures 2.1 and 2.2.
Switching between user mode and privileged mode is controlled by the processor mode bit (MD)
in the status register.
Rev. 5.00, 09/03, page 19 of 760
RENESAS [ RENESAS TECHNOLOGY CORP ]
