MC68HC05X16
Rev. 1
MOTOROLA
3-11
MEMORY AND REGISTERS
3
3.8
Miscellaneous register
POR — Power-on reset bit (see
Section 10.1
)
This bit is set each time the device is powered on. Therefore, the state of the POR bit allows the
user to make a software distinction between a power-on and an external reset. This bit cannot be
set by software and is cleared by writing it to zero.
1 (set)
–
A power-on reset has occurred.
0 (clear) –
No power-on reset has occurred.
INTP, INTN — External interrupt sensitivity options (see
Section 10.2
)
These two bits allow the user to select which edge the IRQ pin and WOI will be sensitive to (see
Table 3-4
). Both bits can be written to only while the I-bit is set, and are cleared by power-on or
external reset, thus the device is initialised with negative edge and low level sensitivity.
INTE — External interrupt enable (see
Section 10.2
)
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.
SFA — Slow or fast mode selection for PLMA (see
Section 8.1
)
1 (set)
–
Slow mode PLMA (4096 x timer clock period).
0 (clear) –
Fast mode PLMA (256 x timer clock period).
(1) The POR bit is set each time there is a power-on reset.
(2) The state of the WDOG bit after reset is dependent on the mask option selected; 1=watchdog enabled, 0=watchdog disabled.
Address
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
State
on reset
Mscellaneous
$000C
POR
(1)
INTP
INTN
INTE
SFA
SFB
SM WDOG
(2)
u001 000u
Table 3-4
IRQ and WOI sensitivity
INTP
0
0
1
1
INTN
0
1
0
1
IRQ sensitivity
WOI interrupt options
Positive edge and high level sensitive
Positive edge only
Negative edge only
Positive and negative edge sensitive
Negative edge and low level sensitive
Negative edge only
Positive edge only
Positive and negative edge sensitive