This actually is in the processor manual
5.3.7 Stack Protection
The Rabbit 6000 provides stack overflow and underflow protection. Low and high logical address limits
can be set in STKLLR and STKHLR; a Priority 3 stack-violation interrupt occurs when a stack-based
write occurs within the 16 bytes below the upper limit or within the 16 bytes above the lower limit. Note
that the writes will still occur even if they are within the 16 bytes surrounding the limits, but the interrupt
can serve as a warning to the application that the stack is in danger of being over or underrun.
The stack checking can be enabled or disabled by writing to STKCR