Application Notes; Notes On Stack Area Use - Hitachi H8/3937 Series Hardware Manual

3.4

Application Notes

3.4.1

Notes on Stack Area Use

When word data is accessed in the H8/3937 Series and H8/3937R 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.
→
SP
SP set to H'FEFF
Notation:
PC : Upper byte of program counter
H
PC : Lower byte of program counter
L
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.
80
→
SP
BSR instruction
Stack accessed beyond SP
→
PC SP
H
PC
L
MOV. B R1L, @–R7
Contents of PC are lost
R1L H'FEFC
PC H'FEFD
L
H'FEFF
H