Interrupt System
The T8xc51Rx2 have a total of 8 interrupt vectors: two external interrupts (INT0 and
INT1), three timer interrupts (timers 0, 1 and 2), the serial port interrupt, Keyboard inter-
rupt and the PCA global interrupt. These interrupts are shown in Figure 19.
Figure 19. Interrupt Control System
INT0
IE0
TF0
INT1
IE1
TF1
PCA IT
RI
TI
IPH, IPL
3
0
3
0
3
0
3
0
3
0
3
0
High Priority
Interrupt
Interrupt
Polling
Sequence, Decreasing from
High to Low Priority
TF2
3
EXF2
0
3
KBD IT
0
Individual Enable
Global Disable
Low Priority
Interrupt
Each of the interrupt sources can be individually enabled or disabled by setting or clear-
ing a bit in the Interrupt Enable register (Table 36 and Table 34). This register also
contains a global disable bit, which must be cleared to disable all interrupts at once.
Each interrupt source also can be individually programmed to one out of four priority lev-
els by setting or clearing a bit in the Interrupt Priority register (Table 37) and in the
Interrupt Priority High register (Table 35 and Table 36) shows the bit values and priority
levels associated with each combination.
46 AT80C51RD2/AT83C51Rx2
4113B–8051–03/05