Motorola MPC8260 User Manual

MOTOROLA

Chapter 4.  System Interface Unit (SIU)  

4-13

In addition to the FCC/MCC/SCC relative priority option, SICR[HP] can be used to specify
one interrupt source as having highest priority. This interrupt remains within the same
interrupt level as the other interrupt controller interrupts, but is serviced before any other
interrupt in the table. 

If the highest priority feature is not used, select the interrupt request in XSIU1 to be the
highest priority interrupt; the standard interrupt priority order is used. SICR[HP] can be
updated dynamically to allow the user to change a normally low priority source into a high
priority-source for a certain period. 

By programming the SIU mask registers, SIMR_H and SIMR_L, the user can mask
interrupt requests to the core. Each SIMR bit corresponds an interrupt source. To enable an
interrupt, write a one to the corresponding SIMR bit. When a masked interrupt source has
a pending interrupt request, the corresponding SIPNR bit is set, even though the interrupt
is not generated to the core. The user can mask all interrupt sources to implement a polling
interrupt servicing scheme. 

When an interrupt source has multiple interrupting events, the user can individually mask
these events by programming a mask register within that block. Table 4-2 shows which
interrupt sources have multiple interrupting events. Figure 4-9 shows an example of how
the masking occurs, using an SCC as an example.