HD64F3642AHV Datasheet, PDF (100/551 Pages) Renesas Technology Corp – Old Company Name in Catalogs and Other Documents

Section 3 Exception Handling
3.4 Application Notes
3.4.1 Notes on Stack Area Use
When word data is accessed in the H8/3644 Group, the least significant bit of the address is
regarded as 0. Access to the stack always takes place in word size, so the stack pointer (SP: R7)
should never indicate an odd address. Use PUSH Rn (MOV.W Rn, @–SP) or POP Rn (MOV.W
@SP+, Rn) to save or restore register values.
Setting an odd address in SP may cause a program to crash. An example is shown in figure 3.6.
SP ^→
SP ^→
PC H
PC L
SP ^→
R1L
PC _L
H'FEFC
H'FEFD
H'FEFF
BSR instruction
MOV. B R1L, @–R7
SP set to H'FEFF
Stack accessed beyond SP Contents of PC_H are lost
Legend:
PC_H: Upper byte of program counter
PC_L: Lower byte of program counter
R1L: General register R1L
SP: Stack pointer
Figure 3.6 Operation when Odd Address Is Set in SP
When CCR contents are saved to the stack during interrupt exception handling or restored when
RTE is executed, this also takes place in word size. Both the upper and lower bytes of word data
are saved to the stack; on return, the even address contents are restored to CCR while the odd
address contents are ignored.
Rev. 6.00 Sep 12, 2006 page 78 of 526
REJ09B0326-0600