C515A_9708 Datasheet, PDF (133/182 Pages) Siemens Semiconductor Group – 8-Bit CMOS Microcontroller

Interrupt System
C515A
7.2 Interrupt Priority Level Structure
The following table shows the interrupt grouping of the C515A interrupt sources.
Table 7-1
Interrupt Source Structure
Interrupt Associated Interrupts
Group _{High Priority}
1
External interrupt 0
2
Timer 0 overflow
3
External interrupt 1
4
Timer 1 overflow
5
Serial channel interrupt
6
Timer 2 interrupt
Low Priority
A/D converter interrupt
External interrupt 2
External interrupt 3
External interrupt 4
External interrupt 5
External interrupt 6
Priority
High
Low
Each pair of interrupt sources can be programmed individually to one of four priority levels by setting
or clearing one bit in the special function register IP0 and one in IP1. A low-priority interrupt can be
interrupted by a high-priority interrupt, but not by another interrupt of the same or a lower priority. An
interrupt of the highest priority level cannot be interrupted by another interrupt source.
lf two or more requests of different priority leveis are received simultaneously, the request of the
highest priority is serviced first. lf requests of the same priority level are received simultaneously, an
internal polling sequence determines which request is to be serviced first. Thus, within each priority
level there is a second priority structure determined by the polling sequence, as follows.
– Within one interrupt group the “left“ interrupt is serviced first
– The interrupt groups are serviced from top to bottom of the table.
Semiconductor Group
7-12
1997-08-01