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3.1.7.1 Reset
Upon an external chip reset, the IDMA channel immediately aborts the channel operation,
returns to the idle state, and clears CSR and CMR (including the STR bit). If a bus cycle is
in progress when reset is detected, the cycle is terminated, the control and address/data
pins are three-stated, and bus ownership is released. The IDMA can also be reset by RST
in the CMR.
3.1.7.2 Bus Error
When a fatal error occurs during a bus cycle, a bus error exception is used to abort the cycle
and systematically terminate that channel's operation. The IDMA terminates the current bus
cycle, signals an error in the CSR, and generates a maskable interrupt. The IDMA clears
STR and waits for a restart of the channel and the negation of BERR before starting any new
bus cycles.
Any data that was previously read from the source into the DHR
will be lost.
3.1.7.3 Halt
IDMA transfer operation may be suspended at any time by asserting HALT to the IDMA. In
response, any bus cycle in progress is completed (after DTACK is asserted), and bus own-
ership is released. No further bus cycles will be started while HALT remains asserted. When
the IDMA is in the middle of an operand transfer when halted and HALT is subsequently ne-
gated, and if a new transfer request is pending, then IDMA will arbitrate for the bus and con-
tinue normal operation.
3.1.7.4 Relinquish and Retry
When HALT and BERR are asserted during a bus cycle, the IDMA terminates the bus cycle,
releases the bus, and suspends any further operation until these signals are negated. When
HALT and BERR are negated, the IDMA will arbitrate for the bus, re-execute the interrupted
bus cycle, and continue normal operation.
3.2 INTERRUPT CONTROLLER
The IMP interrupt controller accepts and prioritizes both internal and external interrupt re-
quests and generates a vector number during the CPU interrupt acknowledge cycle. Inter-
rupt nesting is also provided so that an interrupt service routine of a lower priority interrupt
may be suspended by a higher priority interrupt request. The interrupt controller block dia-
gram is shown in Figure 3-2.
The on-chip interrupt controller has the following features:
• Two Operational Modes: Normal and Dedicated
• Eighteen Prioritized Interrupt Sources (Internal and External)
• A Fully Nested Interrupt Environment
• Unique Vector Number for Each Internal/External Source Generated
• Three Interrupt Request and Interrupt Acknowledge Pairs
MOTOROLA
NOTE
MC68302 USER'S MANUAL
System Integration Block (SIB)
3-15
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