5 interrupt priorities – Texas Instruments MSC1210 User Manual
Page 113
Interrupt Priorities
10-7
Interrupts
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 0033
H
—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 (B8
H
) or EIP (F8
H
) 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
−
BF
H
Undefined
6
−
BE
H
Undefined
5
−
BD
H
Undefined
4
PS
BC
H
Serial Interrupt Priority
3
PT1
BB
H
Timer 1 Interrupt Priority
2
PX1
BA
H
External 1 Interrupt Priority
1
PT0
B9
H
Timer 0 Interrupt Priority
0
PX0
B8
H
External 0 Interrupt Priority
Table 10−6.EIP (F8
H
) SFR
Bit
Name
Bit Address
Explanation of Function
7
−
FF
H
Undefined (set to 1)
6
−
FE
H
Undefined (set to 1)
5
−
FD
H
Undefined (set to 1)
4
PWDI
FC
H
Watchdog Interrupt Priority
3
PX5
FB
H
External Interrupt 5 Priority
2
PX4
FA
H
External Interrupt 4 Priority
1
PX3
F9
H
External Interrupt 3 Priority
0
PX2
F8
H
External Interrupt 2 Priority