COP8-REF-AM datasheet(41/83 Pages) NSC

41 / 83 page

13.0 Power Saving Features

(Continued)

13.5.2 Low Speed Idle Mode

In the IDLE mode, program execution stops and power

consumption is reduced to a very low level as with the HALT

mode. However, the low speed oscillator, IDLE Timer (Timer

T0), and Clock Monitor continue to operate, allowing real

time to be maintained. The device remains IDLE for a se-

lected amount of time up to 2 seconds, and then automati-

cally exits the IDLE mode and returns to normal program

execution using the low speed clock.

The device is placed in the IDLE mode under software

control by setting the IDLE bit (bit 6 of the Port G data

The IDLE Timer window is selectable from one of five values,

0.125 seconds, 0.25 seconds, 0.5 seconds, 1 second, and

2 seconds. Selection of this value is made through the ITMR

The IDLE mode uses the on-chip IDLE Timer (Timer T0) to

keep track of elapsed time in the IDLE state. The IDLE Timer

runs continuously at the low speed clock rate, whether or not

the device is in the IDLE mode. Each time the bit of the timer

associated with the selected window toggles, the T0PND bit

is set, an interrupt is generated (if enabled), and the device

exits the IDLE mode if in that mode. If the IDLE Timer

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

Any time the IDLE Timer window length is changed there is

the possibility of generating a spurious IDLE Timer interrupt

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 Section 12.1 TIMER T0

(IDLE TIMER).

20006324

FIGURE 20. Multi-Input Wake-Up Logic

COP8-REF-AM 数据表(PDF) 41 Page - National Semiconductor (TI)

COP8-REF-AM 数据表(HTML) 41 Page - National Semiconductor (TI)

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83

数据表下载