H8S2245 datasheet(108/818 Pages) RENESAS

108 / 818 page

Section 2 CPU

Rev.3.00 Mar. 26, 2007 Page 66 of 772

REJ09B0355-0300

2.10

Usage Notes

2.10.1

TAS Instruction

Only register ER0, ER1, ER4, or ER5 should be used when using the TAS instruction. The TAS

instruction is not generated by the Renesas Technology 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.

2.10.2

STM/LDM Instruction

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 Technology H8S or H8/300 Series C/C++ Compiler, the STM/LDM instruction

including ER7 is not created.

2.10.3

Bit Manipulation Instructions

When a register that includes write-only bits is manipulated by a bit manipulation instruction,

there are cases where the bits manipulated are not manipulated correctly or bits unrelated to the

bits manipulated are changed.

When a register containing write-only bits is read, the value read is either a fixed value or an

undefined value. This means that the bit manipulation instructions that use the value of bits read in

their operation (BNOT, BTST, BAND, BIAND, BOR, BIOR, BXOR, BIXOR, BLD, and BILD)

will not perform correct bit operations.

Also, bit manipulation instructions that perform a write operation on the data read after the

calculation (BSET, BCLR, BNOT, BST, and BIST) may change bits unrelated to the bits

manipulated. Thus extreme care is required when performing bit manipulation instructions on

registers that include write-only bits.

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