COP688CL Datasheet, PDF (20/40 Pages) National Semiconductor (TI) – General Description

Multi-Input Wakeup
The Multi-Input Wakeup feature is used to return (wakeup)
the device from either the HALT or IDLE modes Alternately
Multi-Input Wakeup Interrupt feature may also be used to
generate up to 8 edge selectable external interrupts
Figure 10 shows the Multi-Input Wakeup logic
The Multi-Input Wakeup feature utilizes the L Port The user
selects which particular L port bit (or combination of L Port
bits) will cause the device to exit the HALT or IDLE modes
The selection is done through the Reg WKEN The Reg
WKEN is an 8-bit read write register which contains a con-
trol bit for every L port bit Setting a particular WKEN bit
enables a Wakeup from the associated L port pin
The user can select whether the trigger condition on the
selected L Port pin is going to be either a positive edge (low
to high transition) or a negative edge (high to low transition)
This selection is made via the Reg WKEDG which is an 8-
bit control register with a bit assigned to each L Port pin
Setting the control bit will select the trigger condition to be a
negative edge on that particular L Port pin Resetting the bit
selects the trigger condition to be a positive edge Changing
an edge select entails several steps in order to avoid a
pseudo Wakeup condition as a result of the edge change
First the associated WKEN bit should be reset followed by
the edge select change in WKEDG Next the associated
WKPND bit should be cleared followed by the associated
WKEN bit being re-enabled
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 pro-
gram would be as follows
RBIT 5 WKEN
SBIT 5 WKEDG
RBIT 5 WKPND
SBIT 5 WKEN
If the L port bits have been used as outputs and then
changed to inputs with Multi-Input Wakeup Interrupt a safe-
ty procedure should also be followed to avoid inherited
pseudo wakeup conditions After the selected L port bits
have been changed from output to input but before the as-
sociated WKEN bits are enabled the associated edge se-
lect bits in WKEDG should be set or reset for the desired
edge selects followed by the associated 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-In-
put 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
corresponding 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 has the
responsibility of clearing the pending flags before attempt-
ing to enter the HALT mode
The WKEN WKPND and WKEDG are all read write regis-
ters 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
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FIGURE 10 Multi-Input Wake Up Logic
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