COP888GD datasheet(19/42 Pages) NSC

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Power Save Modes (Continued)

IDLE MODE

The device is placed in the IDLE mode by writing a “1” to the

IDLE flag (G6 data bit). In this mode, all activities, except the

associated on-board oscillator circuitry, the WATCHDOG

logic, the clock monitor and the IDLE Timer T0, are stopped.

The power supply requirements of the microcontroller in this

mode of operation are typically around 30% of normal power

requirement of the microcontroller.

As with the HALT mode, the device can be returned to nor-

mal operation with a reset, or with a Multi-Input Wakeup from

the L Port.

The microcontroller may also be awakened from the IDLE

mode after a selectable amount of time up to 65,536 instruc-

tion cycles, or 65.536 milliseconds with a 1 MHz instruction

clock frequency.

The IDLE timer period is selectable from one of five values,

4k, 8k, 16k, 32k or 64k instruction cycles. Selection of this

value is made through the ITMR register.

The user has the option of being interrupted with a transition

on the thirteenth bit of the IDLE Timer T0. The interrupt can

be enabled or disabled via the T0EN control bit. Setting the

T0EN flag enables the interrupt and vice versa.

The user can enter the IDLE mode with the Timer T0 inter-

rupt enabled. In this case, when the T0PND bit gets set, the

device will first execute the Timer T0 interrupt service routine

and then return to the instruction following the “Enter Idle

Mode” instruction.

Alternatively, the user can enter the IDLE mode with the

IDLE Timer T0 interrupt disabled. In this case, the device will

resume normal operation with the instruction immediately

following the “Enter IDLE Mode” instruction.

The IDLE timer cannot be started or stopped under software

control, and it is not memory mapped, so it cannot be read or

written by the software. Its state upon Reset is unknown.

Therefore, if the device is put into the IDLE mode at an arbi-

trary time, it will stay in the IDLE mode for somewhere be-

tween 1 and the selected number of instruction cycles.

Upon reset the ITMR register is cleared and selects the

4,096 instruction cycle tap of the Idle Timer.

Note: It is necessary to program two NOP instructions following both the set

HALT mode and set IDLE mode instructions. These NOP instructions

are necessary to allow clock resynchronization following the HALT or

IDLE modes.

For more information on the IDLE Timer and its associated

interrupt, see the description in the Timers Section.

Multi-Input Wakeup

The Multi-Input Wakeup feature is ued 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 12 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 en-

ables 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 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

DS100076-13

FIGURE 12. Multi-Input Wake Up Logic

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