Hi Gerry,
Coldfire exception processing is explained in detail in the interrupt controller module chapter of the user guides, but it can be a bit confusing.
There are a number of steps that you need to complete to enable, trigger and service interrupts properly.
1.You need to configure the peripheral so that it generates interrupts for the condition you are looking for. This usually involves setting register flags for the peripheral.
2. You then unmask the interrupt source in the interrupt controller and set a unique level and priority for that source.
3. When the interrupt fires, the interrupt controller module identifies the source of the interrupt and the vector for that source. If the interrupt source is not masked, it will then call the interrupt service routine pointed to by the vector. All interrupts at or below the level of this source are automatically masked, but your ISR can mask higher levels by setting the CPU's status register mask. The interrupt controller uses the priority to decide which interrupt to service first when more than one interrupt is active simultaneously.
Specifically for the case you talk about, I suspect that you need to unmask the interrupt in the interrupt controller, but you should write a specific ISR and don't use the catch-all asm_exception_handler.
Cheers,
Paul.