at89c51ac3-s3sim ATMEL Corporation, at89c51ac3-s3sim Datasheet - Page 114

• Manufacturer Part Number: at89c51ac3-s3sim
• Description: At89c51ac3 Enhanced 8-bit Microcontroller With 64kb Flash Memory
• Manufacturer: ATMEL Corporation

114
AT89C51AC3
Each of the interrupt sources can be individually enabled or disabled by setting or clear-
ing a bit in the Interrupt Enable register. This register also contains a global disable bit
which must be cleared to disable all the interrupts at the same time.
Each interrupt source can also be individually programmed to one of four priority levels
by setting or clearing a bit in the Interrupt Priority registers. The Table below shows the
bit values and priority levels associated with each combination.
Table 63. Priority Level Bit Values
A low-priority interrupt can be interrupted by a high priority interrupt but not by another
low-priority interrupt. A high-priority interrupt cannot be interrupted by any other interrupt
source.
If two interrupt requests of different priority levels are received simultaneously, the
request of the 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, see Table 64.
Table 64. Interrupt priority Within level
external interrupt (INT0)
external interrupt (INT1)
PCA (CF or CCFn)
Interrupt Name
UART (RI or TI)
Timer0 (TF0)
Timer1 (TF1)
Timer2 (TF2)
SPI interrupt
ADC (ADCI)
IPH.x
0
0
1
1
Interrupt Address Vector
IPL.x
0003h
000Bh
0013h
001Bh
0033h
0023h
002Bh
0043h
0053h
0
1
0
1
Interrupt Level Priority
Priority Number
4383D–8051–02/08
3 (Highest)
0 (Lowest)
1
2
1
2
3
4
5
6
7
8
9