.
Table 4. Interrupt Enable (IE) Register
(MSB)
EA
–
–
ES
Enable Bit = 1 enables the interrupt.
Enable Bit = 0 disables the interrupt.
(LSB)
ET1
EX1
ET0
EX0
Symbol
Position
Function
EA
IE.7
Disables all interrupts. If EA = 0, no interrupt is
acknowledged. If EA = 1, each interrupt source is
individually enabled or disabled by setting or clearing
its enable bit.
–
IE.6
Reserved
–
IE.5
Reserved
ES
IE.4
Serial Port interrupt enable bit
ET1
IE.3
Timer 1 interrupt enable bit
EX1
IE.2
External interrupt 1 enable bit
ET0
IE.1
Timer 0 interrupt enable bit
EX0
IE.0
External interrupt 0 enable bit
User software should never write 1s to reserved bits, because they may be used in future AT89
products.
Figure 1. Interrupt Sources
0
INT0
IE0
1
TF0
0
INT1
IE1
1
TF1
TI
RI
10 AT89LS51
3053A–8051–05/02