mc68336 Freescale Semiconductor, Inc, mc68336 Datasheet - Page 25

• Manufacturer Part Number: mc68336
• Description: An Introduction To The Mc68331 And Mc68332
• Manufacturer: Freescale Semiconductor, Inc

Provide for negation of the signal within the service routine, and avoid writing to the SR during execution of
the level seven interrupt service routine.
2.10.6 Checklist for External Interrupt Acknowledge
• Is the desired pin configured as an interrupt pin instead of an I/O pin?
• Was the starting address of the interrupt routine written to the vector offset address?
• Is the IARB field in the SIMCR a unique, non-zero value between $1 and $F?
• Is the IPL field in the CPU status register set to a value lower than the desired interrupt level?
• Is the IACK cycle terminated with AVEC or DSACK?
• Does the interrupt request signal negate inside the exception handler?
MC68331/332
M68331/332TUT/D
If the IRQ7 signal is asserted and the IPL field is written during execution of the interrupt service routine.
This is true even when the mask is re-written to $7.
The interrupt pins are dual-function pins. Their initial configuration is determined by the state of data
bus pin nine at the release of reset. After reset, their configuration is determined by the port F pin as-
signment register.
The CPU must be told where the interrupt service routine begins. See 4.1.1 Exceptions for a more
detailed explanation.
All interrupting modules must have a unique, non-zero value in the IARB field
The CPU will not recognize an interrupt that is at the same level or lower than the value in the IPL field.
Level seven is the only exception to this rule; it is always recognized.
The IACK cycle must be terminated by assertion of the AVEC or DSACK signals, or a chip-select circuit
must be configured to assert AVEC or DSACK internally.
It is a good idea to control negation of the interrupt in software. The interrupt should be negated before
the RTE instruction.
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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