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MC80F0104/0204
Preliminary
86
Mar. 2005 Ver 0.2
18.4 External Interrupt
The external interrupt on INT0, INT1, INT2 and INT3 pins
are edge triggered depending on the edge selection register
IEDS (address 0EE
H
) as shown in Figure 18-7 .
The edge detection of external interrupt has three transition
activated mode: rising edge, falling edge, and both edge.
Figure 18-7 External Interrupt Block Diagram
INT0 ~ INT3 are multiplexed with general I/O ports (R11,
R12, R03, R00). To use as an external interrupt pin, the bit
of port selection register PSR0 should be set to “1” corre-
spondingly.
Example:
To use as an INT0 and INT2
:
;
**** Set external interrupt port as pull-up state.
LDM
PU1,#0000_0101B
;
;
**** Set port as an external interrupt port
LDM
PSR0,#0000_0101B
;
;
**** Set Falling-edge Detection
LDM
IEDS,#0001_0001B
:
Response Time
The INT0 ~ INT3 edge are latched into INT0IF ~ INT3IF
at every machine cycle. The values are not actually polled
by the circuitry until the next machine cycle. If a request is
active and conditions are right for it to be acknowledged, a
hardware subroutine call to the requested service routine
will be the next instruction to be executed. The DIV itself
takes twelve cycles. Thus, a minimum of twelve complete
machine cycles elapse between activation of an external
interrupt request and the beginning of execution of the first
instruction of the service routine.
Figure 18-8 shows interrupt response timings.
Figure 18-8 Interrupt Response Timing Diagram
INT0IF
INT0 pin
INT0 INTERRUPT
INT1IF
INT1 pin
INT1 INTERRUPT
INT2IF
INT2 pin
INT2 INTERRUPT
IEDS
[0EEH]
INT3IF
INT3 pin
INT3 INTERRUPT
Edge selection
Register
2
2
2
2
01
10
11
01
10
11
01
10
11
01
10
11
Interrupt
goes
active
Interrupt
latched
Interrupt
processing
Interrupt
routine
8 f
XIN
max. 12 f
XIN
Содержание MC80C0104
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