Motorola MC68VZ328 - Manual (Page 157)

Programming Model
Interrupt Controller 9-7
9.6 Programming Model
This section describes registers that you may need to configure so that the interrupt controller can properly
process interrupts, generate vector numbers, and post interrupts to the core.
NOTE:
When programmed as edge-triggered interrupts, all external interrupts
(INT[3:0], IRQ1, IRQ2, IRQ3, and IRQ6) can be cleared by writing a 1 to
the corresponding status bit in the interrupt status register (ISR). When
programmed as level-triggered interrupts, these interrupts are cleared at
the requesting sources. All interrupts from internal peripheral devices are
level-triggered interrupts to the interrupt handler, and they are cleared at
the requesting sources.
9.6.1 Interrupt Vector Register
The interrupt vector register (IVR) is used to program the upper 5 bits of the interrupt vector number.
During the interrupt acknowledge cycle, the lower 3 bits, encoded from the interrupt level, are combined
with the upper 5 bits to form an 8-bit vector number. The CPU uses the vector number to generate a vector
address. During system startup, this register should be configured so that the MC68VZ328’s external and
internal interrupts can be handled properly by their software handlers. If an interrupt occurs before the IVR
has been programmed, the interrupt vector number 0x0F is returned to the CPU as an uninitialized
interrupt, which has the interrupt vector 0x3C.
The register bit assignments are shown in the following register display, and their settings are described in
Table 9-3.
IVR Interrupt Vector Register 0x(FF)FFF300
BIT 7 6 5 4 3 2 1 BIT 0
VECTOR
TYPE rw rw rw rw rw
RESET
0 0 0 0 0 0 0 0
0x00
Table 9-3. Interrupt Vector Register Description
Name Description Settings
VECTOR
Bits 7–3 Vector Number—This field represents the upper 5 bits of the inter-
rupt vector number. See description.
Reserved
Bits 2–0 Reserved These bits are reserved
and should be set to 0.