t89c51rd2-slscl ATMEL Corporation, t89c51rd2-slscl Datasheet - Page 39

• Manufacturer Part Number: t89c51rd2-slscl
• Description: 0 To 40 Mhz Flash Programmable 8-bit Microcontroller
• Manufacturer: ATMEL Corporation

4243G–8051–05/03
A low-priority interrupt can be interrupted by a high priority interrupt, but not by another
low-priority interrupt. A high-priority interrupt can’t be interrupted by any other interrupt
source.
If two interrupt requests of different priority levels are received simultaneously, the
request of higher priority level is serviced. If interrupt requests of the same priority level
are received simultaneously, an internal polling sequence determines which request is
serviced. Thus within each priority level there is a second priority structure determined
by the polling sequence.
Table 23. IE Register
IE - Interrupt Enable Register (A8h)
Reset Value = 0000 0000b
Bit addressable
Number
Bit
EA
7
6
5
4
3
2
1
0
7
Mnemonic Description
EX1
EX0
ET2
ET1
ET0
Bit
EA
EC
ES
EC
6
Enable All interrupt bit
Clear to disable all interrupts.
Set to enable all interrupts.
If EA=1, each interrupt source is individually enabled or disabled by setting or
clearing its own interrupt enable bit.
PCA interrupt enable bit
Clear to disable . Set to enable.
Timer 2 overflow interrupt Enable bit
Clear to disable timer 2 overflow interrupt.
Set to enable timer 2 overflow interrupt.
Serial port Enable bit
Clear to disable serial port interrupt.
Set to enable serial port interrupt.
Timer 1 overflow interrupt Enable bit
Clear to disable timer 1 overflow interrupt.
Set to enable timer 1 overflow interrupt.
External interrupt 1 Enable bit
Clear to disable external interrupt 1.
Set to enable external interrupt 1.
Timer 0 overflow interrupt Enable bit
Clear to disable timer 0 overflow interrupt.
Set to enable timer 0 overflow interrupt.
External interrupt 0 Enable bit
Clear to disable external interrupt 0.
Set to enable external interrupt 0.
ET2
5
ES
4
ET1
3
EX1
2
T89C51RD2
ET0
1
EX0
0
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