COP8SE datasheet(21/47 Pages) NSC

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7.0 Power Saving Features (Continued)

7.3 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 17 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 register WKEN. The regis-

ter WKEN is an 8-bit read/write register, which contains a

control 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 se-

lected 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 register 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

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 be-

ing 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 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 WK-

PND. The respective bits of the WKPND register will be set

on the occurrence of the selected trigger edge on the corre-

sponding Port L pin. The user has the responsibility of clear-

ing 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 en-

abled and pending. Consequently, the user must clear the

pending flags before attempting to enter the HALT mode.

WKEN and WKEDG are all read/write registers, and are

cleared at reset. WKPND register contains random value af-

ter reset.

DS100973-26

FIGURE 16. Wakeup from IDLE

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