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Chapter 4 Interrupt (S12ZINTV0)
MC9S12ZVM Family Reference Manual Rev. 1.3
138
Freescale Semiconductor
4.4
Functional Description
The INT 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.
4.4.1
S12Z Exception Requests
The CPU handles both reset requests and interrupt requests. The INT module 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 relative priority of pending interrupt requests.
4.4.2
Interrupt Prioritization
After system reset all I-bit maskable interrupt requests are configured to be enabled, are set up to be
handled by the CPU and have a pre-configured priority level of 1. Exceptions to this rule are the non-
maskable interrupt requests and the spurious interrupt vector request at (vector base + 0x0001DC) which
cannot be disabled, are always handled by the CPU and have a fixed priority levels. A priority level of 0
effectively disables the associated I-bit maskable 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 priority level must be set to non zero.
b) The priority level must be greater than the current interrupt processing level in the condition
code register (CCW) of the CPU (PRIOLVL[2:0] > IPL[2:0]).
3. The I-bit in the condition code register (CCW) of the CPU must be cleared.
4. There is no access violation interrupt request pending.
5. There is no SYS, SWI, SPARE, TRAP, Machine Exception or XIRQ request pending.
1
0
1
Priority level 5
1
1
0
Priority level 6
high
1
1
1
Priority level 7
Table 4-7. Interrupt Priority Levels
Priority
PRIOLVL2
PRIOLVL1
PRIOLVL0
Meaning