Cpu Operating Modes; Normal Mode - Renesas H8S Series Hardware Manual

Section 2 CPU
2.2

CPU Operating Modes

The H8S/2000 CPU has two operating modes: normal and advanced. Normal mode supports a
maximum 64 kbytes address space. Advanced mode supports a maximum 16 Mbytes address
space. The mode is selected by the LSI's mode pins.
2.2.1

Normal Mode

The exception vector table and stack have the same structure as in the H8/300 CPU in normal
mode.
• Address space
Linear access to a maximum address space of 64 kbytes is possible.
• Extended registers (En)
The extended registers (E0 to E7) can be used as 16-bit registers, or as the upper 16-bit
segments of 32-bit registers.
When extended register En is used as a 16-bit register it can contain any value, even when the
corresponding general register (Rn) is used as an address register. (If general register Rn is
referenced in the register indirect addressing mode with pre-decrement (@–Rn) or post-
increment (@Rn+) and a carry or borrow occurs, the value in the corresponding extended
register (En) will be affected.)
• Instruction set
All instructions and addressing modes can be used. Only the lower 16 bits of effective
addresses (EA) are valid.
• Exception vector table and memory indirect branch addresses
In normal mode, the top area starting at H'0000 is allocated to the exception vector table. One
branch address is stored per 16 bits. The exception vector table in normal mode is shown in
figure 2.1. For details of the exception vector table, see section 4, Exception Handling.
The memory indirect addressing mode (@@aa:8) employed in the JMP and JSR instructions
uses an 8-bit absolute address included in the instruction code to specify a memory operand
that contains a branch address. In normal mode, the operand is a 16-bit (word) operand,
providing a 16-bit branch address. Branch addresses can be stored in the top area from H'0000
to H'00FF. Note that this area is also used for the exception vector table.
• Stack structure
In normal mode, when the program counter (PC) is pushed onto the stack in a subroutine call
in normal mode, and the PC and condition-code register (CCR) are pushed onto the stack in
exception handling, they are stored as shown in figure 2.2. The extended control register
(EXR) is not pushed onto the stack. For details, see section 4, Exception Handling.
Rev. 3.00 Jul. 14, 2005 Page 22 of 986
REJ09B0098-0300