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MC68HC05B6
Rev. 4
MOTOROLA
9-9
RESETS AND INTERRUPTS
9
9.2.3.2
Miscellaneous register
Note:
The bits shown shaded in the above representation are explained individually in the
relevant sections of this manual. The complete register plus an explanation of each bit
INTP, INTN — External interrupt sensitivity options
These two bits allow the user to select which edge the IRQ pin is sensitive to as shown in
Table 9-3.Both bits can be written to only while the I-bit is set, and are cleared by power-on or external reset.
Therefore the device is initialised with negative edge and low level sensitivity.
INTE — External interrupt enable
1 (set)
–
External interrupt function (IRQ) enabled.
0 (clear) –
External interrupt function (IRQ) disabled.
The INTE bit can be written to only while the I-bit is set, and is set by power-on or external reset,
thus enabling the external interrupt function.
Table 9-3 describes the various triggering options available for the IRQ pin, however it is important
to re-emphasize here that in order to avoid any conict and spurious interrupt, it is only possible to
change the external interrupt options while the I-bit is set. Any attempt to change the external
interrupt option while the I-bit is clear will be unsuccessful. If an external interrupt is pending, it will
automatically be cleared when selecting a different interrupt option.
Note:
If the external interrupt function is disabled by the INTE bit and an external interrupt is
sensed by the edge detector circuitry, then the interrupt request is latched and the
interrupt stays pending until the INTE bit is set. The internal latch of the external
interrupt is cleared in the rst part of the service routine (except for the low level
Address
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
State
on reset
Miscellaneous
$000C
POR
INTP
INTN
INTE
SFA
SFB
SM
WDOG ?001 000?
Table 9-3 IRQ sensitivity
INTP
INTN
IRQ sensitivity
0
Negative edge and low level sensitive
0
1
Negative edge only
1
0
Positive edge only
1
Positive and negative edge sensitive
TPG
111
05B6Book Page 9 Tuesday, April 6, 1999 8:24 am