ST92F124/F150/F250 - INTERRUPTS
ARBITRATION MODES (Cont’d)
Examples
Example 1
In the following two examples, three interrupt re-
quests with different priority levels (2, 3 & 4) occur
simultaneously during the interrupt 5 service rou-
tine.
In the first example, (simplest case, Figure 46) the
eiinstruction is not used within the interrupt serv-
ice routines. This means that no new interrupt can
be serviced in the middle of the current one. The
interrupt routines will thus be serviced one after
another, in the order of their priority, until the main
program eventually resumes.
Figure 46. Simple Example of a Sequence of Interrupt Requests with:
- Concurrent mode selected and
- IEN unchanged by the interrupt routines
INTERRUPT 2 HAS PRIORITY LEVEL 2
INTERRUPT 3 HAS PRIORITY LEVEL 3
INTERRUPT 4 HAS PRIORITY LEVEL 4
INTERRUPT 5 HAS PRIORITY LEVEL 5
0
1
2
3
4
5
6
7
Priority Level of
Interrupt Request
INT 2
CPL = 7
INT 3
CPL = 7
INT 2
INT 3
INT 4
INT 4
CPL = 7
INT 5
CPL = 7
ei
INT 5
MAIN
MAIN
CPL = 7
CPL is set to 7
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