C167CS datasheet(78/517 Pages) INFINEON

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C167CS

Derivatives

The Central Processing Unit (CPU)

User’s Manual

4-28

V2.0, 2000-07

The Stack Overflow Pointer STKOV

This non-bit addressable register is compared against the SP register after each

operation, which pushes data onto the system stack (e.g. PUSH and CALL instructions

or interrupts) and after each subtraction from the SP register. If the content of the SP

will occur.

Since the least significant bit of register STKOV is tied to ‘0’ and bits 15 through 12 are

tied to ‘1’ by hardware, the STKOV register can only contain values from F000H to

FFFEH.

The Stack Overflow Trap (entered when (SP) < (STKOV)) may be used in two different

ways:

• Fatal error indication treats the stack overflow as a system error through the

associated trap service routine. Under these circumstances data in the bottom of the

stack may have been overwritten by the status information stacked upon servicing the

stack overflow trap.

• Automatic system stack flushing allows to use the system stack as a ‘Stack Cache’

for a bigger external user stack. In this case register STKOV should be initialized to a

value, which represents the desired lowest Top of Stack address plus 12 according to

the selected maximum stack size. This considers the worst case that will occur, when

a stack overflow condition is detected just during entry into an interrupt service

routine. Then, six additional stack word locations are required to push IP, PSW, and

CSP for both the interrupt service routine and the hardware trap service routine.

More details about the stack overflow trap service routine and virtual stack management

are given in Chapter 22.

STKOV

Stack Overflow Reg.

SFR (FE14H/0AH)

Reset Value: FA00H

9876

543210

1111

stkov

Bit

Function

stkov

Modifiable portion of register STKOV

Specifies the lower limit of the internal system stack.

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