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Bus Operation
7-34 M68060 USER’S MANUAL MOTOROLA
instruction boundary (following any higher priority exception). The IPEND signal negates
after the interrupt acknowledge bus cycle.
IPEND is intended to provide status information, and must not be used to replace the inter-
rupt acknowledge cycle. As such, normal applications do not rely on IPEND to disable inter-
rupts. Applications that use IPEND as a replacement for the interrupt acknowledge cycle are
neither recommended nor supported.
The MC68060 takes an interrupt exception for a pending interrupt within one instruction
boundary after processing any other pending exception with a higher priority. Thus, the
MC68060 executes at least one instruction in an interrupt exception handler before recog-
nizing another interrupt request. The following paragraphs describe the various kinds of
interrupt acknowledge bus cycles that can be executed as part of interrupt exception pro-
cessing. Table 7-4 provides a summary of the possible interrupt acknowledge terminations
and the exception processing results. Note that TRA must always be negated for proper
operation in the MC68040 acknowledge termination mode.
Figure 7-26. Assertion of IPEND
Table 7-4. Interrupt Acknowledge Termination Summary
Acknowledge
Termination
Mode
TA TEA TRA AVEC Termination Condition
Either High High High Don’t Care Insert Wait States
MC68040 High Low High Don’t Care Take Spurious Interrupt Exception
Native-MC68060 Don’t Care Low Don’t Care Don’t Care
Either Low High High High Register Vector Number on D7–D0 and Take Inter-
rupt Exception
Either Low High High Low Take Autovectored Interrupt Exception
MC68040 Low Low High Don’t Care Retry Interrupt Acknowledge Cycle
Native-MC68060 Don’t Care High Low Don’t Care
MC68040 Don’t Care Don’t Care Low Don’t Care Illegal Combination, Unsupported
CLK
IPL2–IPL0
IPEND
COMPARE REQUEST WITH MASK IN SR
ASSERT IPENDIPLx RECOGNIZED
IPLx SYNCHRONIZED
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