cop8scr9lva8 National Semiconductor Corporation, cop8scr9lva8 Datasheet - Page 43

• Manufacturer Part Number: cop8scr9lva8
• Description: 8-bit Cmos Flash Based Microcontroller With 32k Memory, Virtual Eeprom And Brownoutff
• Manufacturer: National Semiconductor Corporation

13.0 Power Saving Features
interrupt is enabled, the interrupt is serviced before execu-
tion of the main program resumes. (However, the instruction
which was started as the part entered the IDLE mode is
completed before the interrupt is serviced. This instruction
should be a NOP which should follow the enter IDLE instruc-
tion.) The user must reset the IDLE Timer pending flag
(T0PND) before entering the IDLE mode.
As with the HALT mode, this device can also be returned to
normal operation with a Multi-Input Wake-up input.
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
arbitrary time, it will stay in the IDLE mode for somewhere
between 30 µs and the selected time period.
In order to precisely time the duration of the IDLE state, entry
into the IDLE mode must be synchronized to the state of the
IDLE Timer. The best way to do this is to use the IDLE Timer
interrupt, which occurs on every underflow of the bit of the
IDLE Timer which is associated with the selected window.
Another method is to poll the state of the IDLE Timer pending
bit T0PND, which is set on the same occurrence. The Idle
Timer interrupt is enabled by setting bit T0EN in the ICNTRL
register.
Any time the IDLE Timer window length is changed there is
the possibility of generating a spurious IDLE Timer interrupt
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 register WKEDG, which is an
8-bit control register with a bit assigned to each L Port pin.
(Continued)
FIGURE 21. Multi-Input Wake-Up Logic
43
by setting the T0PND bit. The user is advised to disable
IDLE Timer interrupts prior to changing the value of the
ITSEL bits of the ITMR Register and then clear the T0PND
bit before attempting to synchronize operation to the IDLE
Timer.
As with the HALT mode, it is necessary to program two
NOP’s to allow clock resynchronization upon return from the
IDLE mode. The NOP’s are placed either at the beginning of
the IDLE Timer interrupt routine or immediately following the
“enter IDLE mode” instruction.
For more information on the IDLE Timer and its associated
interrupt, see the description in the Section 6.1, Timer T0
(IDLE Timer).
13.6 MULTI-INPUT WAKE-UP
The Multi-Input Wake-up feature is used to return (wake-up)
the device from either the HALT or IDLE modes. Alternately
Multi-Input Wake-up/Interrupt feature may also be used to
generate up to 8 edge selectable external interrupts.
Figure 21 shows the Multi-Input Wake-up logic.
The Multi-Input Wake-up 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 reg-
ister 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 Wake-up from the associated 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
Wake-up condition as a result of the edge change. First, the
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