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Chapter 16 Interrupt (S12XINTV1)

MC9S12XDP512 Data Sheet, Rev. 2.21

Freescale Semiconductor

607

16.4

Functional Description

The XINT module processes all exception requests to be serviced by the CPU module. These exceptions

include interrupt vector requests and reset vector requests. Each of these exception types and their overall

priority level is discussed in the subsections below.

16.4.1

S12X Exception Requests

The CPU handles both reset requests and interrupt requests. The XINT contains registers to conﬁgure the

priority level of each I bit maskable interrupt request which can be used to implement an interrupt priority

scheme. This also includes the possibility to nest interrupt requests. A priority decoder is used to evaluate

the priority of a pending interrupt request.

16.4.2

Interrupt Prioritization

After system reset all interrupt requests with a vector address lower than or equal to (vector base + 0x00F2)

are enabled, are set up to be handled by the CPU and have a pre-conﬁgured priority level of 1. The

exception to this rule is the spurious interrupt vector request at (vector base + 0x0010) which cannot be

disabled, is always handled by the CPU and has a ﬁxed priority level of 7. A priority level of 0 effectively

disables the associated interrupt request.

If more than one interrupt request is conﬁgured to the same interrupt priority level the interrupt request

with the higher vector address wins the prioritization.

The following conditions must be met for an I bit maskable interrupt request to be processed.

1. The local interrupt enabled bit in the peripheral module must be set.

2. The setup in the conﬁguration register associated with the interrupt request channel must meet the

following conditions:

a) The XGATE request enable bit must be 0 to have the CPU handle the interrupt request.

b) The priority level must be set to non zero.

c) The priority level must be greater than the current interrupt processing level in the condition

code register (CCR) of the CPU (PRIOLVL[2:0] > IPL[2:0]).

3. The I bit in the condition code register (CCR) of the CPU must be cleared.

4. There is no SWI, TRAP, or XIRQ request pending.

NOTE

All non I bit maskable interrupt requests always have higher priority than

I bit maskable interrupt requests. If an I bit maskable interrupt request is

interrupted by a non I bit maskable interrupt request, the currently active

interrupt processing level (IPL) remains unaffected. It is possible to nest

non I bit maskable interrupt requests, e.g., by nesting SWI or TRAP calls.

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