
Memory
Random-Access Memory (RAM)
MC68HLC908QY/QT Family — Rev. 2
Data Sheet
MOTOROLA
Memory
31
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2.5 Random-Access Memory (RAM)
The 128 bytes of random-access memory (RAM) are located at addresses
$0080–$00FF. 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)
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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