COP87L88GD Datasheet, PDF (16/39 Pages) National Semiconductor (TI) – 8-Bit CMOS OTP Microcontrollers with 16k or 32k Memory and 8-Channel A/D with Prescaler

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.
FIGURE 12. Multi-Input Wake Up Logic
DS012526-13
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
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