The LPC2200 have 3 timer: Timer0,Time1,PWM timer. But the ARTX just can use Timer0 or Timer1 as ARTX Kernel timer. In some situation, we need the capture or match funtion of the Timer0 and Timer1 but needn't PWM. You know, both Timer0 and Timer1 have 4 capture channel, some times we even can use the capture funtion as external interrupt. That mean if use the ARTX we will lost 4 channel of external interrupt. So if the ARTX Kernel timer can choose PWM timer that will help much.