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Rev. 1.00
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Standard 8051 8-Bit Flash MCU
HT85F2260/HT85F2270/HT85F2280
Interrupts
Interrupt Priority
In case of simultaneous requests, the following table shows the priority that is applied. The
interrupts can be assigned into groups. Higher priority interrupts can stop the lower priority
interrupts. All interrupts are categorised into 19 groups with 4 priority levels. In cases where
both higher priority and lower priority interrupts are enabled and where a higher priority and
lower priority interrupt occurs simultaneously, the higher priority interrupt will always have
priority and will therefore be serviced first. Suitable masking of the individual interrupts using the
interrupt registers can prevent simultaneous occurrences. Each interrupt source can be individually
programmed to one of four priority levels by setting or clearing bits in the interrupt priority
registers: IP0, IP1, IP2, IP3, IP0H, IP1H, IP2H and IP3H. IP0, IP1, IP2 and IP3 hold the low order
priority bits and IP0H, IP1H, IP2H and IP3H hold the high priority bits for each interrupt.
If the priority level is the same for different groups, then an internal polling sequence determines
which interrupt request is serviced. The polling sequence is based on the vector address; an
interrupt with a lower vector address has higher priority than an interrupt with a higher vector
address. Note that the polling sequence is only used to resolve interrupt requests of the same
priority level.
Priority Levels
The accompanying table illustrates the interrupt priority level assigned by the corresponding
IPnH.x and IPn.x bits (n=0~3).
IPnH.x
IPn.x
Priority Level
Note
1
1
Level 3
Highest P�io�it�
1
0
Level �
↓
0
1
Level 1
↓
0
0
Level 0
Lowest P�io�it�
If the interrupt levels are assigned the same priority level by the IPnH.x and IPn.x bits, the interrupt
priority is followed by the accompanying table.