C508_01 Datasheet, PDF (210/267 Pages) Infineon Technologies AG – 8-Bit CMOS Microcontroller

C508
Interrupt System
7.2.2
Interrupt Request Flags
The request flags for the various interrupt sources are located in several Special
Function Registers. This section describes the locations and meanings of these interrupt
request flags in detail.
Special Function Register TCON (Address 88_H)
Reset Value: 00_H
MSB
LSB
Bit No. 8F_H 8E_H 8D_H 8C_H 8B_H 8A_H 89_H 88_H
88_H TF1 TR1 TF0 TR0 IE1 IT1 IE0 IT0 TCON
The shaded bits are not used for interrupt control.
Bit
Function
TF1
Timer 1 overflow flag
Set by hardware on timer/counter 1 overflow. Cleared by hardware when
processor vectors to interrupt routine.
TF0
Timer 0 overflow flag
Set by hardware on timer/counter 0 overflow. Cleared by hardware when
processor vectors to interrupt routine.
IE1
External Interrupt 1 request flag
Set by hardware when external interrupt 1 edge is detected. Cleared by
hardware when processor vectors to interrupt routine.
IT1
External Interrupt 1 level/edge trigger control flag
If IT1 = 0, low level triggered external interrupt 1 is selected.
If IT1 = 1, falling edge triggered external interrupt 1 is selected.
IE0
External Interrupt 0 request flag
Set by hardware when external interrupt 0 edge is detected. Cleared by
hardware when processor vectors to interrupt routine.
IT0
External Interrupt 0 level/edge trigger control flag
If IT0 = 0, low level triggered external interrupt 0 is selected.
If IT0 = 1, falling edge triggered external interrupt 0 is selected.
Each of the external interrupts 0 and 1 (P3.2/INT0 and P3.3/INT1) can be level-
activated or negative transition-activated, depending on bits IT0 and IT1 in register
TCON. The flags that actually generate these interrupts are bits IE0 and lE1 in TCON.
When an external interrupt is generated, the flag which generated this interrupt is cleared
by the hardware when the service routine is vectored to – but, only if the interrupt was
transition-activated. lf, however, the interrupt was level-activated, the requesting
external source controls the request flag directly, rather than the on-chip hardware.
User’s Manual
7-12
2001-05