External Interrupt (IRQ)
Functional Description
MC68HC908SR12MC68HC08SR12 — Rev. 5.0
Data Sheet
Freescale Semiconductor
External Interrupt (IRQ)
337
When an interrupt pin is edge-triggered only, the interrupt remains set
until a vector fetch, software clear, or reset occurs.
When an interrupt pin is both falling-edge and low-level-triggered, the
interrupt remains set until both of the following occur:
Vector fetch or software clear
Return of the interrupt pin to logic 1
The vector fetch or software clear may occur before or after the interrupt
pin returns to logic 1. As long as the pin is low, the interrupt request
remains pending. A reset will clear the latch and the MODE1 control bit,
thereby clearing the interrupt even if the pin stays low.
When set, the IMASK bit in the INTSCR mask all external interrupt
requests. A latched interrupt request is not presented to the interrupt
priority logic unless the IMASK bit is clear.
NOTE:
The interrupt mask (I) in the condition code register (CCR) masks all
interrupt requests, including external interrupt requests.
Figure 19-2. IRQ1 Block Diagram
ACK1
IMASK1
DQ
CK
CLR
IRQ1
HIGH
INTERRUPT
TO MODE
SELECT
LOGIC
IRQ1
FF
REQUEST
VDD
MODE1
VOLTAGE
DETECT
SYNCHRO-
NIZER
IRQ1F
TO CPU FOR
BIL/BIH
INSTRUCTIONS
VECTOR
FETCH
DECODER
INTERN
AL
ADDRESS
BUS
RESET
V
DD
INTERNAL
PULLUP
DEVICE
IRQ1