C167CS datasheet(117/517 Pages) INFINEON

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C167CS

Derivatives

Interrupt and Trap Functions

User’s Manual

5-34

V2.0, 2000-07

External NMI Trap

Whenever a high to low transition on the dedicated external NMI pin (Non-Maskable

Interrupt) is detected, the NMI flag in register TFR is set and the CPU will enter the NMI

trap routine. The IP value pushed on the system stack is the address of the instruction

following the one after which normal processing was interrupted by the NMI trap.

Note: The NMI pin is sampled with every CPU clock cycle to detect transitions.

Stack Overflow Trap

Whenever the stack pointer is decremented to a value which is less than the value in the

stack overflow register STKOV, the STKOF flag in register TFR is set and the CPU will

enter the stack overflow trap routine. Which IP value will be pushed onto the system

stack depends on which operation caused the decrement of the SP. When an implicit

decrement of the SP is made through a PUSH or CALL instruction, or upon interrupt or

trap entry, the IP value pushed is the address of the following instruction. When the SP

is decremented by a subtract instruction, the IP value pushed represents the address of

the instruction after the instruction following the subtract instruction.

For recovery from stack overflow it must be ensured that there is enough excess space

on the stack for saving the current system state (PSW, IP, in segmented mode also CSP)

twice. Otherwise, a system reset should be generated.

Stack Underflow Trap

Whenever the stack pointer is incremented to a value which is greater than the value in

the stack underflow register STKUN, the STKUF flag is set in register TFR and the CPU

will enter the stack underflow trap routine. Again, which IP value will be pushed onto the

system stack depends on which operation caused the increment of the SP. When an

implicit increment of the SP is made through a POP or return instruction, the IP value

pushed is the address of the following instruction. When the SP is incremented by an

add instruction, the pushed IP value represents the address of the instruction after the

instruction following the add instruction.

Undefined Opcode Trap

When the instruction currently decoded by the CPU does not contain a valid C167CS

opcode, the UNDOPC flag is set in register TFR and the CPU enters the undefined

opcode trap routine. The IP value pushed onto the system stack is the address of the

instruction that caused the trap.

This can be used to emulate unimplemented instructions. The trap service routine can

examine the faulting instruction to decode operands for unimplemented opcodes based

on the stacked IP. In order to resume processing, the stacked IP value must be

incremented by the size of the undefined instruction, which is determined by the user,

before a RETI instruction is executed.

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