The ARM peripheral bus

Timer0    free running micro-second counter (TIMER command)
Timer1    used on ARMweb or with ON TIMER
Timer1    setup as 1msec timer, may be reprogrammed
Timer1  , Timer2 and Timer3 used for HWPWM on ARMmite or ARMexpress LITE
Uart0      UART for debug/download
Uart1      Not Used unless requested by user with BAUD1
PWM     used when HWPWM is engaged on PROplus, SuperPRO
I2C         Not Used
SPI        reserved
RTC       used for time-keeping

            
FIQ           not used
ISR0          UART0
ISR2          PWM -- only used by ARMweb
ISR3          UART1 if RXD1, TXD1 used
ISR4          EINT0 if ON EINT0 used            
ISR5          EINT1 if ON EINT1 used

            
ISR6          EINT2 if ON EINT2 used
ISR7          TIMER1 if ON TIMER used

ARMweb has  EINT0 connected to ENC28J60,
but it is not used and available to the user. 

            
ARMweb firmware also uses EINT2 for remote debugging.

            
ISR21         UART0 
ISR22         UART1

If a function is not included in the BASIC code the interrupt is available, for instance ON TIMER uses TIMER0 interrupt and RXD1 uses the UART1 interrupt.

In Idle just the CPU clock stops and any interrupt will wake it.

Background Tasks

Except for the ARMweb, the only background tasks are interrupt handlers for UART0 and UART1. UART1 is not active until the BAUD1 function is called.