XC886/888CLM
Interrupt System
User’s Manual
5-8
V1.3, 2010-02
Interrupt System, V 1.0
5.1
Interrupt Structure
An interrupt event source may be generated from the on-chip peripherals or from
external. Detection of interrupt events is controlled by the respective on-chip peripherals.
Interrupt status flags are available for determining which interrupt event has occurred,
especially useful for an interrupt node which is shared by several event sources. Each
interrupt node has a global enable/disable bit. In most cases, additional enable bits are
provided for enabling/disabling particular interrupt events.
In general, the XC886/888 has two interrupt structures distinguished mainly by the
manner in which the pending interrupt request (one per interrupt vector/source going
directly to the core) is generated (due to the events) and cleared.
Common among these two interrupt structures is the interrupt masking bit, EA, which is
used to globally enable or disable all interrupt requests (except NMI) to the core.
Resetting bit EA to 0 only masks the pending interrupt requests from the core, but does
not block the capture of incoming interrupt requests.
5.1.1
Interrupt Structure 1
, the interrupt event will set the interrupt status flag
which doubles as a pending interrupt request to the core. An active pending interrupt
request will interrupt the core only if its corresponding interrupt node is enabled. Once
an interrupt node is serviced (interrupt acknowledged), its pending interrupt request
(represented by the interrupt status flag) may be automatically cleared by hardware (the
core).
Figure 5-7
Interrupt Structure 1
For the XC886/888, interrupt sources Timer 0, Timer 1, external interrupt 0 and external
interrupt 1 (each have a dedicated interrupt node) will have their respective interrupt
status flags TF0, TF1, IE0 and IE1 in register TCON cleared by the core once their
corresponding pending interrupt request is serviced. In the case that an interrupt node is
set
pending
interrupt
request
interrupt source
enable bit
interrupt status
flag
interrupt
event
software
clear
clear
interrupt
acknowledge
(from core)
AND
EA bit
to core
*
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