COP8ACC5 datasheet(19/41 Pages) NSC

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Multi-Input Wakeup (Continued)

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

; Disable MIWU

SBIT 5, WKEDG

; Change edge polarity

RBIT 5, WKPND

; Reset pending flag

SBIT 5, WKEN

; 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

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.)

DS012865-13

FIGURE 12. Multi-Input Wake Up Logic

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