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Timer Module Timing Diagrams

9.5.2 Turning Off Any Timer Not in Use

For applications not requiring all of the timers, it is possible to turn off any timer not in use. Individual timers are shut off by resetting the TE bit to zero for that individual timer and setting the ES[1:0] bits to 01 for that individual timer. These bits are located in register TCR01 or TCR2, depending on which timer is to be turned off.

9.5.3 Lowering the Timer Frequency

For applications requiring a timer to execute at a low frequency, less power is consumed if the timer is clocked using the prescaler clock instead of the Phi clock.

9.5.4 Running the Timer in Wait Mode

Overall power consumption on the DSP56824 can be reduced by using the wait mode of the DSP56800 core. It is possible to place the chip in wait mode for a predetermined amount of time. A timer is enabled and begins counting immediately before executing a WAIT instruction. When the timer reaches zero, a signal is generated that interrupts the DSP56800 core and brings it out of wait mode. All modes of operation in the timer module are available in wait mode.

9.5.5 Running the Timer in Stop Mode

Overall power consumption on the DSP56824 can be greatly reduced using the stop mode of the DSP56800 core. It is possible to place the chip in stop mode for a predetermined amount of time by setting up Timer 2 using the prescaler clock as input. This timer is enabled and begins counting. Then the DSP56800 core executes a STOP instruction. When Timer 2 reaches zero, a signal is generated that wakes up the DSP core and brings it out of stop mode.

NOTE:

The prescaler clock is the only clock available to the timer module that is active in stop mode. The TIO pin cannot be used as an event counter in stop mode. Also, only Timer 2 is capable of bringing the DSP56824 out of stop mode, and it performs this function independently of the bits in the IPR—see Section 3.3.1, “DSP56824 Interrupt Priority Register (IPR),” on page 3-14—or the value of the OIE control bit—see Section 9.1.1.3, “Overflow Interrupt Enable (OIE)—Bit 12, Bit 4.”

9.6 Timer Module Timing Diagrams

The figures in this section illustrate configurations in which the timer can be enabled, disabled, and used. Figure 9-4 on page 9-16 shows the standard timer operation, and Figure 9-5 on page 9-16 shows a write to the count register after writing the preload register when the timer is disabled.

 

Timers

9-15

Timers

TE

Event

Preload

Register

Count

Register

Overflow

Interrupt

TE

Event

Preload

Register

Value to Write

to the Count

Register

Overflow

Interrupt

Write Enable

Preload Timer

Preload

 

 

 

 

 

 

 

 

 

 

 

 

 

Preload

Preload – 1

 

 

Preload – 2

0

 

 

 

Preload

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

AA0228

Figure 9-4. Standard Timer Operation with Overflow Interrupt

Write

Write

Write

Enable

Preload

Count

Preload

Timer

. . .

Preload Preload

Count

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Preload

 

 

Count

 

 

Count – 1

 

 

Count – 2

0

 

 

 

Preload2

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

AA0229

Figure 9-5. Write to the Count Register with Timer Disabled

9-16

DSP56824 User’s Manual

 

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