Middle Mode - Renesas H8SX/1520 Series Hardware Manual

2.2.2

Middle Mode

The program area in middle mode is extended to 16 Mbytes as compared with that in normal
mode.
• Address Space
The maximum address space of 16 Mbytes can be accessed as a total of the program and data
areas. For individual areas, up to 16 Mbytes of the program area or up to 64 kbytes of the data
area can be allocated.
• 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 the extended register En is used as a 16-bit register (in
other than the JMP and JSR instructions), it can contain any value even when the
corresponding general register Rn is used as an address register. (If the general register Rn is
referenced in the register indirect addressing mode with pre-/post-increment or pre-/post-
decrement and a carry or borrow occurs, however, 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 and the upper eight bits are sign-extended.
• Exception Vector Table and Memory Indirect Branch Addresses
In middle mode, the top area starting at H'000000 is allocated to the exception vector table.
One branch address is stored per 32 bits. The upper eight bits are ignored and the lower 24 bits
are stored. The structure of the exception vector table is shown in figure 2.4.
The memory indirect (@@aa:8) and extended memory indirect (@@vec:7) addressing modes
are used in the JMP and JSR instructions. An 8-bit absolute address included in the instruction
code specifies a memory location. Execution branches to the contents of the memory location.
In middle mode, an operand is a 32-bit (longword) operand, providing a 32-bit branch address.
The upper eight bits are reserved and assumed to be H'00.
• Stack Structure
The stack structure of PC at a subroutine branch and that of PC and CCR at an exception
handling are shown in figure 2.5. The PC contents are saved or restored in 24-bit units.
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Rev. 3.00 Mar. 14, 2006 Page 23 of 804
REJ09B0104-0300
Section 2 CPU