pc87591l National Semiconductor Corporation, pc87591l Datasheet - Page 98

• Manufacturer Part Number: pc87591l
• Description: Lpc Mobile Embedded Controllers
• Manufacturer: National Semiconductor Corporation

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Embedded Controller Modules
4.3
The ICU has 31 channels. It interfaces between the different modules’ interrupt requests and external interrupt requests and
also generates the core interrupt. It generates both maskable and non-maskable interrupts. The ICU has a predetermined
scheme that allocates priority.
4.3.1
Non-Maskable Interrupts (NMI)
Maskable Interrupts
4.3.2
The Interrupt Control Unit (ICU) gathers external non-maskable interrupt (NMI) sources and generates an NMI interrupt to
the core when required.
External NMI Inputs
The ICU processes the PFAIL signal to send to the CR16B NMI input.
Non-Maskable Interrupt Processing
The CR16B core performs an “Interrupt Acknowledge” bus cycle when beginning to process a non-maskable interrupt. The
address associated with this core bus cycle is within the internal core address space and may be monitored as a Core Bus
Monitoring (CBM) clock cycle. For additional details, see “Core Bus Monitoring” on page 82 and Section 4.20.6 on page 273.
After reset, NMI is disabled and must remain disabled until the software initializes the interrupt table, interrupt base and the
interrupt mode.
The PFAIL interrupt is enabled by setting ENLCK bit and remains enabled until a reset occurs. This allows the external NMI
feature to be enabled only after the Interrupt Base Register (IMASK) and the Interrupt Stack Pointer (ISP), in the core, have
been set up.
Alternatively, the external PFAIL interrupt can be enabled by setting EN bit, which remains enabled until an interrupt event
or a reset occurs. The NMISTAT register holds the status of the current pending NMI request. When the bit in NMISTAT is
set to 1, an NMI request to the core is issued. NMISTAT is cleared each time its contents are read. NMI handlers must read
the NMISTAT register to allow new NMI events to occur.
Note that PFAIL status bit in NMISTAT register may be set as a result of transient enable conditions on PFAIL. To avoid an
interrupt to the core, after configuring the PFAIL input for operation, read the NMISTAT register and then enable PFAIL by
writing 1 to EN bit in PFAIL register.
PFAIL Input
The PFAIL signal is an asynchronous input with Schmitt trigger characteristics and an internal synchronization circuit; there-
fore, no external synchronizing circuit is needed. The PFAIL signal generates an interrupt on its falling edge.
4.3.3
The ICU receives level or edge-triggered interrupt request signals from 31 sources and generates a vectored interrupt to the
CR16B core when required. Priority among the interrupt sources (named INT1 to INT31) is fixed. Each interrupt source can
be individually enabled or disabled under software control through:
Gathers all edge-triggered non-maskable interrupt sources
— External Power Fail (PFAIL) interrupt source
Holds the status of the current pending NMI requests
Generates non-maskable interrupt (NMI) to the core
31 active high-level or edge-triggered interrupt sources
Core vectored interrupt mode
Fixed priority among interrupt sources
Individual enable/disable for each interrupt source
Polling support by an interrupt status register
Clear registers for edge-triggered interrupts
ICU interrupt enable registers
Interrupt enable bits in the peripherals that request the interrupts.
INTERRUPT CONTROL UNIT (ICU)
Features
Non-Maskable Interrupt (NMI)
Maskable Interrupts
(Continued)
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