MOTOROLA
Chapter 6. System Configuration and Protection
6-11
Enhanced Interrupt Controller
NOTE
The RCPU takes the system reset exception when an NMI is
asserted, the external interrupt exception for any other asserted
interrupt request, and the decrementer exception when the
decrementer MSB changes from 0 to 1.
Decrementer interrupt request is not a part of the interrupt controller. Each one of the
external pins IRQ[1:7] has its own dedicated assigned priority level. IRQ[0] is also
mapped, but it should be used only as a status bit indicating that IRQ[0] was asserted and
generated NMI interrupt. There are eight additional interrupt priority levels. Each one of
the SIU internal interrupt sources, or any of the peripheral module interrupt sources can be
assigned by software to any one of the eight interrupt priority levels. Thus, a very flexible
interrupt scheme is implemented. The interrupt request signal generated by the interrupt
controller is driven to the RPCU core and to the IRQOUT pin (optionally). This pin may be
used in peripheral mode, when the RCPU is disabled, and the internal modules are accessed
externally. The IMB interrupts are controlled by the UIMB. The IMB provides 32 interrupt
levels, and any interrupt source could be configured to any IMB interrupt level. The UIMB
contains a 32-bit register that holds the IMB interrupt requests, and maps them to the USIU
eight interrupt levels.
NOTE
If one interrupt level was configured to more than one interrupt
source, the software should read the UIPEND register in the
UIMB module, and the particular status bits in order to identify
which interrupt was asserted.
The interrupt controller may be programmed to operate in two modes—a regular mode and
an enhanced mode.
6.4.3
Regular Interrupt Controller Operation
(MPC555/MPC556 Compatible Mode)
In regular operation mode (default setting) the interrupt controller receives interrupt
requests from internal sources, such as timers, PLL lock detector, IMB modules and from
external pins IRQ[0:7]. All the internal interrupt sources may be programmed to drive one
or more of eight U-bus interrupt level lines while the RCPU, upon receiving an interrupt
request, has to read the USIU and UIMB status register in order to determine the interrupt
source.
The SIVEC register contains an 8-bit code representing the unmasked interrupt request
which has the highest priority level. The priority between all interrupt sources for the
regular interrupt controller operation is shown in
Table 6-3.