Datasheet

Memory
MC68HC908QY/QT Family Data Sheet, Rev. 6
32 Freescale Semiconductor
.
2.5 Random-Access Memory (RAM)
Addresses $0080–$00FF are RAM locations. The location of the stack RAM is programmable. The 16-bit
stack pointer allows the stack to be anywhere in the 64-Kbyte memory space.
NOTE
For correct operation, the stack pointer must point only to RAM locations.
Before processing an interrupt, the central processor unit (CPU) uses five bytes of the stack to save the
contents of the CPU registers.
NOTE
For M6805, M146805, and M68HC05 compatibility, the H register is not
stacked.
During a subroutine call, the CPU uses two bytes of the stack to store the return address. The stack
pointer decrements during pushes and increments during pulls.
NOTE
Be careful when using nested subroutines. The CPU may overwrite data in
the RAM during a subroutine or during the interrupt stacking operation.
Table 2-1. Vector Addresses
Vector Priority Vector Address Vector
Lowest
Highest
IF15
$FFDE ADC conversion complete vector (high)
$FFDF ADC conversion complete vector (low)
IF14
$FFE0 Keyboard vector (high)
$FFE1 Keyboard vector (low)
IF13
↓
IF6
— Not used
IF5
$FFF2 TIM overflow vector (high)
$FFF3 TIM overflow vector (low)
IF4
$FFF4 TIM Channel 1 vector (high)
$FFF5 TIM Channel 1 vector (low)
IF3
$FFF6 TIM Channel 0 vector (high)
$FFF7 TIM Channel 0 vector (low)
IF2 — Not used
IF1
$FFFA IRQ
vector (high)
$FFFB IRQ
vector (low)
—
$FFFC SWI vector (high)
$FFFD SWI vector (low)
—
$FFFE Reset vector (high)
$FFFF Reset vector (low)