Datasheet

Section 2 CPU
Page 58 of 846 REJ09B0140-0900 Rev. 9.00
Sep 16, 2010
H8S/2215 Group
2.9 Usage Notes
2.9.1 Note on TAS Instruction Usage
Only register ER0, ER1, ER4, or ER5 should be used when using the TAS instruction. The TAS
instruction is not generated by the Renesas Electronics H8S and H8/300 series C/C++ compilers.
If the TAS instruction is used as a user-defined intrinsic function, ensure that only register ER0,
ER1, ER4, or ER5 is used.
2.9.2 STM/LTM Instruction Usage
With the STM or LDM instruction, the ER7 register is used as the stack pointer, and thus cannot
be used as a register that allows save (STM) or restore (LDM) operation.
With a single STM or LDM instruction, two to four registers can be saved or restored. The
available registers are as follows:
For two registers: ER0 and ER1, ER2 and ER3, or ER4 and ER5
For three registers: ER0 to ER2, or ER4 to ER6
For four registers: ER0 to ER3
For the Renesas Electronics H8S or H8/300 Series C/C++ Compiler, the STM/LDM instruction
including ER7 is not created.
2.9.3 Note on Bit Manipulation Instructions
Using bit manipulation instructions on registers containing write-only bits can result in the bits
that should have been manipulated not being manipulated as intended or in the wrong bits being
manipulated.
Reading data from a register containing write-only bits may return fixed or undefined values.
Consequently, bit manipulation instructions that use the read values to perform operations (BNOT,
BTST, BAND, BIAND, BOR, BIOR, BXOR, BIXOR, BLD, and BILD) will not work properly.
In addition, bit manipulation instructions that write data following operations based on the data
values read (BSET, BCLR, BNOT, BST, and BIST) may change the values of bits unrelated to the
intended bit manipulation. Therefore, caution is necessary when using bit manipulation
instructions on registers containing write-only bits.
The instructions BSET, BCLR, BNOT, BST, and BIST perform the following operations in the
order shown: