hd66100 Renesas Electronics Corporation., hd66100 Datasheet - Page 99

• Manufacturer Part Number: hd66100
• Description: H8/3867 Series
• Manufacturer: Renesas Electronics Corporation.

3.4
3.4.1
When word data is accessed in the H8/3864 Series, 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.
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.
84
SP
SP set to H'FEFF
Notation:
PC
PC
R1L:
SP:
Application Notes
Notes on Stack Area Use
H
L
:
:
Upper byte of program counter
Lower byte of program counter
General register R1L
Stack pointer
Figure 3.6 Operation when Odd Address is Set in SP
BSR instruction
SP
Stack accessed beyond SP
PC
PC
H
L
MOV. B R1L, @–R7
SP
Contents of PC are lost
PC
R1L
L
H
H'FEFC
H'FEFD
H'FEFF