82C836 Datasheet, PDF (83/205 Pages) List of Unclassifed Manufacturers – Single-Chip 386sx AT

Interrupt Controller
End-Of-Interrupt s
Specific Rotation Mode
Specific Rotation allows the system software to reassign priority levels by issuing a
command that redefines the highest priority channel. Figure 7-5 illustrates the result
of a specific rotation command, assigning highest priority to Channel 5.
Figure 7-5. Specific Rotation Mode
Lowest
Highest
Priority Status ₇
6
5
4
3
2
1
0 ^{Before Rotation}
Priority Status ₅
4
3
2
1
0
7
6 ^{After Rotation}
Automatic Rotation Mode
In applications in which a number of equal priority peripherals are requesting interrupts,
Automatic rotation may be used to equalize the priority assignment. In this mode, a
peripheral, after being serviced, is assigned the lowest priority. All peripherals connected
to the controller are serviced at least once in eight interrupt requests to the CPU from the
controller. Automatic rotation occurs, if enabled, due to the occurrence of EOI
(automatic or CPU generated).
Figure 7-6. Automatic Rotation Mode
Before Rotation
IS7 IS6 IS5 IS4 IS3 IS2 IS1 IS0
ISR Status Bit ₀
1
0
1
0
Priority Status ₇
6
5
4
3
2
1
0
Lowest
Highest
After Rotation
IS7 IS6 IS5 IS4 IS3 IS2 IS1 IS0
ISR Status Bit ₀
1
0
Priority Status ₄
3
2
1
0
7
6
5
Lowest
Highest
Chips and Technologies, Inc.
PRELIMINARY
Revision 3.0 7-7