C517A_99 Datasheet, PDF (185/218 Pages) Siemens Semiconductor Group – 8-Bit CMOS Microcontroller

Interrupt System
C517A
7.2 Interrupt Priority Level Structure
The 17 interrupt sources of the C517A are combined in six groups. Table 7-1 lists the structure of
these interrupt groups.
Table 7-1
Interrupt Source Structure
Interrupt Associated Interrupts
Group _{High Priority}
Low Priority
1
External interrupt 0
Serial port 1 interrupt A/D converter interrupt
2
Timer 0 overflow
–
External interrupt 2
3
External interrupt 1
CM0-7 match interrupt External interrupt 3
4
Timer 1 overflow
Compare timer interrupt External interrupt 4
5
Serial port 0 interrupt Match in COMSET
External interrupt 5
6
Timer 2 interrupt
Match in COMCLR
External interrupt 6
Priority
High
Low
Each group 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 itself 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
7-15