MOTOROLA
10-10
MC68HC05X16
Rev. 1
RESETS AND INTERRUPTS
10
10.2.3.1
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
can be found in
Section 3.8
.
INTP, INTN — External interrupt sensitivity options
These two bits allow the user to select which edge the IRQ and WOI pins are sensitive to as shown
in
Table 10-3
. 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.
Interrupt sensitivity options selected by INTP and INTN of the miscellaneous register apply to
external interrupt signal, EI. EI is an OR function of all enabled WOI pins (port B and NWOI) and
of the inverted value of the IRQ pin. When one WOI pin is high, it masks any subsequent edge or
level on any other EI pin (IRQ, port B or NWOI).
INTE — External interrupt enable
1 (set)
–
External interrupt (IRQ) and wired-OR interrupt (WOI) enabled.
0 (clear) –
External interrupt (IRQ) and wired-OR interrupt (WOI) 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 10-3
describes the various triggering options available for the IRQ and WOI pins, however it
is important to re-emphasize here that in order to avoid any conflict and spurious interrupt, it is
possible to change the external interrupt options only 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.
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
u001 000u
Table 10-3
IRQ and WOI sensitivity
INTP
INTN
IRQ sensitivity
WOI interrupt sensitivity
Positive edge and high level
sensitive
Positive edge only
Negative edge only
Positive and negative edge
sensitive
0
0
Negative edge and low level
sensitive
Negative edge only
Positive edge only
Positive and negative edge
sensitive
0
1
1
0
1
1