mc68hc908rc24d Freescale Semiconductor, Inc, mc68hc908rc24d Datasheet - Page 156

• Manufacturer Part Number: mc68hc908rc24d
• Description: M68hc08 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

External Interrupt (IRQ)
14.6 IRQ Module During Break Interrupts
Advance Information
156
NOTE:
The vector fetch or software clear and the return of the IRQ1 pin to
logic 1 may occur in any order. The interrupt request remains pending as
long as the IRQ1 pin is at logic 0. A reset will clear the latch and the
MODE1 control bit, thereby clearing the interrupt even if the pin stays
low.
If the MODE1 bit is clear, the IRQ1 pin is falling-edge-sensitive only. With
MODE1 clear, a vector fetch or software clear immediately clears the
IRQ1 latch.
The IRQF1 bit in the ISCR register can be used to check for pending
interrupts. The IRQF1 bit is not affected by the IMASK1 bit, which makes
it useful in applications where polling is preferred.
Use the BIH or BIL instruction to read the logic level on the IRQ1 pin.
When using the level-sensitive interrupt trigger, avoid false interrupts by
masking interrupt requests in the interrupt routine.
The BCFE bit in the break flag control register (BFCR) enables software
to clear the latch during the break state. See
(BRK). To allow software to clear the IRQ1 latch during a break interrupt,
write a logic 1 to the BCFE bit. If a latch is cleared during the break state,
it remains cleared when the MCU exits the break state.
To protect CPU interrupt flags during the break state, write a logic 0 to
the BCFE bit. With BCFE at logic 0 (its default state), writing to the ACK1
bit in the IRQ status and control register during the break state has no
effect on the IRQ interrupt flags.
•
spurious interrupts due to noise. Setting ACK1 does not affect
subsequent transitions on the IRQ1 pin. A falling edge that occurs
after writing to the ACK1 bit generates another interrupt request.
If the IRQ1 mask bit, IMASK1, is clear, the CPU loads the program
counter with the vector address at locations $FFFA and $FFFB.
Return of the IRQ1 pin to logic 1 — As long as the IRQ1 pin is at
logic 0, IRQ1 remains active.
External Interrupt (IRQ)
Section 18. Break Module
MC68HC908RC24 — Rev. 1.1
Freescale Semiconductor