Philips Semiconductors Preliminary data
P89C51RA2/RB2/RC2/RD2xx80C51 8-bit Flash microcontroller family
8KB/16KB/32KB/64KB ISP/IAP Flash with 512B/512B/512B/1KB RAM
2002 Jul 18
31
Interrupt Priority Structure
The P89C51RA2/RB2/RC2/RD2xx has a 7 source four-level
interrupt structure (see Table 7).
There are 3 SFRs associated with the four-level interrupt. They are
the IE, IP, and IPH. (See Figures 21, 22, and 23.) The IPH (Interrupt
Priority High) register 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 23.
The function of the IPH SFR, 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)
The priority scheme for servicing the interrupts is the same as that
for the 80C51, except there are four interrupt levels rather than two
as on the 80C51. 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
PCA 5 CF, CCFn
n = 0–4
N 33H
SP 6 RI, TI N 23H
T2 7 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 EC PCA interrupt enable bit
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.
SU01290
ET0EX1ET1ESET2ECEA
01234567
Figure 21. IE Registers
