Z8 Encore!
®
64K Series
Product Specification
65
•
•
Executing a Trap instruction
Illegal Instruction 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 were enabled with identical interrupt priority (all as Level 2 interrupts, for
example), then interrupt priority would be assigned from highest to lowest as specified in
turn, always have 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 23. Reset,
Watch-Dog Timer interrupt (if enabled), and Illegal Instruction Trap always have highest
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.
Caution:
The following style of coding to clear bits in the Interrupt Request registers
is
NOT
recommended. All incoming interrupts that are received between
execution of the first LDX command and the last LDX command are lost.
Poor coding style that can result in lost interrupt requests:
LDX r0, IRQ0
AND r0, MASK
LDX IRQ0, r0
To avoid missing interrupts, the following style of coding to clear bits in
the Interrupt Request 0 register is recommended:
Good coding style that avoids lost interrupt requests:
ANDX IRQ0, MASK
Software Interrupt Assertion
Program code can generate interrupts directly. Writing a 1 to the desired bit in the Interrupt
Request register triggers an interrupt (assuming that interrupt is enabled). When the inter-
rupt request is acknowledged by the eZ8 CPU, the bit in the Interrupt Request register is
automatically cleared to 0.
PS019915-1005
Interrupt Controller
ZILOG [ ZILOG, INC. ]
