Texas Instruments MSC1210 manual Interrupt Priorities, 5.IP B8 H SFR, 6.EIP F8 H SFR

Interrupt Priorities

10.5 Interrupt Priorities

The MSC1210 offers three levels of interrupt priority: highest, high, and low. By using interrupt priorities, higher priority may be assigned to certain interrupt conditions. The highest priority is reserved for the auxiliary interrupt that vec- tors through address 0033H—the auxiliary interrupt is always of highest prior- ity and no other interrupt may be assigned that priority.

All other interrupts may be assigned either high or low priority. For example, assume the Timer 1 interrupt has been enabled to be automatically called ev- ery instance Timer 1 overflows. Additionally, the serial interrupt has been en- abled to be called every time a character is received via the serial port. Howev- er, in this case, receiving a character is much more important than the timer interrupt. Therefore, if the Timer 1 interrupt is already executing, the serial in- terrupt must interrupt the Timer 1 interrupt. When the serial interrupt is com- plete, control passes back to the Timer 1 interrupt and finally back to the main program. This may be accomplished by assigning a high priority to the serial interrupt and a low priority to the Timer 1 interrupt.

Interrupt priorities are controlled by the IP (B8H) or EIP (F8H) SFRs. These SFRs have the following formats, as shown in Table 10−5 and Table 10−6.

Table 10−5.IP (B8 H ) SFR

Bit	Name	Bit Address	Explanation of Function
7	−	BFH	Undefined
6	−	BEH	Undefined
5	−	BDH	Undefined
4	PS	BCH	Serial Interrupt Priority
3	PT1	BBH	Timer 1 Interrupt Priority
2	PX1	BAH	External 1 Interrupt Priority
1	PT0	B9H	Timer 0 Interrupt Priority
0	PX0	B8H	External 0 Interrupt Priority

Table 10−6.EIP (F8 H ) SFR

Bit	Name	Bit Address	Explanation of Function
7	−	FFH	Undefined (set to 1)
6	−	FEH	Undefined (set to 1)
5	−	FDH	Undefined (set to 1)
4	PWDI	FCH	Watchdog Interrupt Priority
3	PX5	FBH	External Interrupt 5 Priority
2	PX4	FAH	External Interrupt 4 Priority
1	PX3	F9H	External Interrupt 3 Priority
0	PX2	F8H	External Interrupt 2 Priority

Interrupts 10-7