Datasheet

Random-Access Memory (RAM)
MC68HC908JL3E Family Data Sheet, Rev. 4
Freescale Semiconductor 27
2.4 Random-Access Memory (RAM)
Addresses $0080 through $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.
Within page zero are 128 bytes of RAM. Because the location of the stack RAM is programmable, all page
zero RAM locations can be used for I/O control and user data or code. When the stack pointer is moved
from its reset location at $00FF, direct addressing mode instructions can access efficiently all page zero
RAM locations. Page zero RAM, therefore, provides ideal locations for frequently accessed global
variables.
Before processing an interrupt, the CPU uses five bytes of the stack to save the contents of the CPU
registers.
NOTE
For M6805 compatibility, the H register is not stacked.
Table 2-1. Vector Addresses
Vector Priority INT Flag Address Vector
Lowest
Highest
—
$FFD0
↓
$FFDD
Not Used
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)