Z8 Encore! XP® 4K Series
Product Specification
53
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Writing a 1 to the IRQEbit in the Interrupt Control register
Interrupts are globally disabled by any of the following actions:
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Execution of a DI (Disable Interrupt) instruction
eZ8 CPU acknowledgement of an interrupt service request from the interrupt controller
Writing a 0 to the IRQEbit in the Interrupt Control register
Reset
Execution of a Trap instruction
Illegal Instruction Trap
Primary Oscillator Fail Trap
Watch-Dog Oscillator Fail Trap
Interrupt Vectors and Priority
The interrupt controller supports three levels of interrupt priority. Level 3 is the highest
priority, Level 2 is the second highest priority, and Level 1 is the lowest priority. If all of
the interrupts are enabled with identical interrupt priority (all as Level 2 interrupts, for
example), the interrupt priority is assigned from highest to lowest as specified in Table 33
on page 51. Level 3 interrupts are always assigned higher priority than Level 2 interrupts
which, in turn, always are assigned higher priority than Level 1 interrupts. Within each
interrupt priority level (Level 1, Level 2, or Level 3), priority is assigned as specified in
Table 33, above. Reset, Watch-Dog Timer interrupt (if enabled), Primary Oscillator Fail
Trap, Watchdog Oscillator Fail Trap, and Illegal Instruction Trap always have highest
(level 3) priority.
Interrupt Assertion
Interrupt sources assert their interrupt requests for only a single system clock period (sin-
gle pulse). When the interrupt request is acknowledged by the eZ8 CPU, the correspond-
ing bit in the Interrupt Request register is cleared until the next interrupt occurs. Writing a
0 to the corresponding bit in the Interrupt Request register likewise clears the interrupt
request.
The following coding style that clears bits in the Interrupt Request registers is NOT rec-
ommended. All incoming interrupts received between execution of the first LDX com-
mand and the final LDX command are lost.
Caution:
Poor coding style that can result in lost interrupt requests:
LDX r0, IRQ0
AND r0, MASK
LDX IRQ0, r0
PS022815-0206
Interrupt Controller
ZILOG [ ZILOG, INC. ]
