COP8ACC5 Datasheet, PDF (19/41 Pages) National Semiconductor (TI) – 8-Bit CMOS ROM Based Microcontrollers with 4k Memory and High Resolution A/D

Multi-Input Wakeup (Continued)
DS012865-13
FIGURE 12. Multi-Input Wake Up Logic
An example may serve to clarify this procedure. Suppose we
wish to change the edge select from positive (low going high)
to negative (high going low) for L Port bit 5, where bit 5 has
previously been enabled for an input interrupt. The program
would be as follows:
RBIT 5, WKEN
SBIT 5, WKEDG
RBIT 5, WKPND
SBIT 5, WKEN
; Disable MIWU
; Change edge polarity
; Reset pending flag
; Enable MIWU
If the L port bits have been used as outputs and then
changed to inputs with Multi-Input Wakeup/Interrupt, a safety
procedure should also be followed to avoid wakeup condi-
tions. After the selected L port bits have been changed from
output to input but before the associated WKEN bits are en-
abled, the associated edge select bits in WKEDG should be
set or reset for the desired edge selects, followed by the as-
sociated WKPND bits being cleared.
This same procedure should be used following reset, since
the L port inputs are left floating as a result of reset.
The occurrence of the selected trigger condition for
Multi-Input Wakeup is latched into a pending register called
WKPND. The respective bits of the WKPND register will be
set on the occurrence of the selected trigger edge on the cor-
responding Port L pin. The user has the responsibility of
clearing these pending flags. Since WKPND is a pending
register for the occurrence of selected wakeup conditions,
the device will not enter the HALT mode if any Wakeup bit is
both enabled and pending. Consequently, the user must
clear the pending flags before attempting to enter the HALT
mode.
WKEN, WKPND and WKEDG are all read/write registers,
and are cleared at reset.
PORT L INTERRUPTS
Port L provides the user with an additional eight fully select-
able, edge sensitive interrupts which are all vectored into the
same service subroutine.
The interrupt from Port L shares logic with the wake up cir-
cuitry. The register WKEN allows interrupts from Port L to be
individually enabled or disabled. The register WKEDG speci-
fies the trigger condition to be either a positive or a negative
edge. Finally, the register WKPND latches in the pending
trigger conditions.
The GIE (Global Interrupt Enable) bit enables the interrupt
function.
A control flag, LPEN, functions as a global interrupt enable
for Port L interrupts. Setting the LPEN flag will enable inter-
rupts and vice versa. A separate global pending flag is not
needed since the register WKPND is adequate.
Since Port L is also used for waking the device out of the
HALT or IDLE modes, the user can elect to exit the HALT or
IDLE modes either with or without the interrupt enabled. If he
elects to disable the interrupt, then the device will restart ex-
ecution from the instruction immediately following the in-
struction that placed the microcontroller in the HALT or IDLE
modes. In the other case, the device will first execute the in-
terrupt service routine and then revert to normal operation.
(See HALT MODE for clock option wakeup information.)
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