P89C51RB2HXX Datasheet, PDF (21/56 Pages) NXP Semiconductors – 80C51 8-bit Flash microcontroller family

Philips Semiconductors
80C51 8-bit Flash microcontroller family
16KB/32KB/64KB ISP/IAP Flash with 512B/512B/1KB RAM
Product data
P89C51RB2/P89C51RC2/
P89C51RD2Hxx
Interrupt Priority Structure
The P89C51RB2/RC2/RD2Hxx has a 7 source four-level interrupt
structure (see Table 6).
There are 3 SFRs associated with the four-level interrupt. They are
the IE, IP, and IPH. (See Figures 10, 11, and 12.) 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 12.
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
0
1
1
0
1
1
INTERRUPT PRIORITY LEVEL
Level 0 (lowest priority)
Level 1
Level 2
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 6. Interrupt Table
SOURCE
POLLING PRIORITY
X0
1
T0
2
X1
3
T1
4
PCA
5
SP
6
T2
7
NOTES:
1. L = Level activated
2. T = Transition activated
REQUEST BITS
IE0
TP0
IE1
TF1
CF, CCFn
n = 0–4
RI, TI
TF2, EXF2
HARDWARE CLEAR?
N (L)¹ Y (T)²
Y
N (L) Y (T)
Y
N
N
N
VECTOR ADDRESS
03H
0BH
13H
1BH
33H
23H
2BH
7
6
5
4
3
2
1
0
IE (0A8H)
EA
EC
ET2
ES
ET1 EX1 ET0 EX0
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
Figure 10. IE Registers
2002 May 24
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