Philips Semiconductors Product specification
80C31/80C32
80C51 8-bit microcontroller family
128/256 byte RAM ROMless low voltage (2.7V–5.5V),
low power, high speed (33 MHz)
2000 Aug 07
17
Interrupt Priority Structure
The 80C31 and 80C32 have a 6-source four-level interrupt
structure. They are the IE, IP and IPH. (See Figures 10, 11, and 12.)
The IPH (Interrupt Priority High) register that makes the four-level
interrupt structure possible. The IPH is located at SFR address B7H.
The structure of the IPH register and a description of its bits is
shown in Figure 12.
The function of the IPH SFR is simple and when combined with the
IP SFR determines the priority of each interrupt. The priority of each
interrupt is determined as shown in the following table:
PRIORITY BITS
IPH.x IP.x
0 0 Level 0 (lowest priority)
0 1 Level 1
1 0 Level 2
1 1 Level 3 (highest priority)
An interrupt will be serviced as long as an interrupt of equal or
higher priority is not already being serviced. If an interrupt of equal
or higher level priority is being serviced, the new interrupt will wait
until it is finished before being serviced. If a lower priority level
interrupt is being serviced, it will be stopped and the new interrupt
serviced. When the new interrupt is finished, the lower priority level
interrupt that was stopped will be completed.
Table 7. Interrupt Table
SOURCE POLLING PRIORITY REQUEST BITS HARDWARE CLEAR? VECTOR ADDRESS
X0 1 IE0 N (L)
1
Y (T)
2
03H
T0 2 TP0 Y 0BH
X1 3 IE1 N (L) Y (T) 13H
T1 4 TF1 Y 1BH
SP 5 RI, TI N 23H
T2 6 TF2, EXF2 N 2BH
NOTES:
1. L = Level activated
2. T = Transition activated
EX0IE (0A8H)
Enable Bit = 1 enables the interrupt.
Enable Bit = 0 disables it.
BIT SYMBOL FUNCTION
IE.7 EA Global disable bit. If EA = 0, all interrupts are disabled. If EA = 1, each interrupt can be individually
enabled or disabled by setting or clearing its enable bit.
IE.6 — Not implemented. Reserved for future use.
IE.5 ET2 Timer 2 interrupt enable bit.
IE.4 ES Serial Port interrupt enable bit.
IE.3 ET1 Timer 1 interrupt enable bit.
IE.2 EX1 External interrupt 1 enable bit.
IE.1 ET0 Timer 0 interrupt enable bit.
IE.0 EX0 External interrupt 0 enable bit.
SU00571
ET0EX1ET1ESET2—EA
01234567
Figure 10. IE Registers
