C167CR_00 Datasheet, PDF(75/464 Page) Infineon Technologies AG – 16-Bi t Single-Chip Microcont roller

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C167CR_00 Datasheet, PDF (75/464 Pages) Infineon Technologies AG – 16-Bi t Single-Chip Microcont roller

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C167CR

Derivatives

The Central Processing Unit (CPU)

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

register is less than the content of the STKOV register, a stack overflow hardware trap

will occur.

Since the least significant bit of register STKOV is tied to â0â and bits 15 through 12 are

tied to â1â by hardware, the STKOV register can only contain values from F000H to

FFFEH.

STKOV

Stack Overflow Reg.

SFR (FE14H/0AH)

15 14 13 12 11 10 9 8 7 6 5

Reset value:FA00H

43210

1111

stkov

0

rrrr

rw

Bit

stkov

Function

Modifiable portion of register STKOV

Specifies the lower limit of the internal system stack.

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

ways:

â¢ 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.

â¢ Automatic system stack flushing allows to use the system stack as a âStack Cacheâ

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 21.

Userâs Manual

4-28

V3.1, 2000-03

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