EFM32G-DK3550【PDF 297/467 页】KIT DEVELOPMENT EFM32 GECKO

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21.3.5.2 Continuous Output Generation

Example 21.2. LETIMER Continuous Output Generation

In some scenarios, it might be desired to make LETIMER generate a continuous waveform. Very simple

constant waveforms can be generated without the repeat counter as shown in Figure 21.6 (p. 295) , but

to generate changing waveforms, using the repeat counter and buffer registers can prove advantageous.

For the example in Figure 21.10 (p. 297) , the goal is to produce a pulse train consisting of 3 sequences

with the following properties:

? 3 pulses with periods of 3 cycles

? 4 pulses with periods of 2 cycles

? 2 pulses with periods of 3 cycles

Figure 21.10. LETIMER Continuous Operation

Write

COMP1 = 2

Initial configuration,

REPB just written

REP1 = 2

Stop,

final values

COMP1

COMP0

CNT

REP0

1

2

0

3

1

2

2

3

1

2

1

3

1

2

0

3

1

2

2

2

1

2

1

2

1

2

0

2

1

2

2

1

1

2

1

1

1

2

0

1

1

1

1

4

1

1

0

4

1

1

1

3

2

1

0

3

2

1

1

2

2

1

0

2

2

1

1

1

2

1

0

1

2

2

2

2

2

2

1

2

2

2

0

2

2

2

2

1

2

2

1

1

2

2

0

1

2

2

0

0

REP1

4

4

4

4

4

4

4

4

4

4

4 u 4 u 4 u 2

2

2

2

2

2 u 2 u 2 u 2 u 2 u 2 u 2 u

Int. flags set

UFIF

UFIF

UFIF

UFIF UFIF

UFIF

UFIF

UFIF

LFACLK LETIMERn

LETn_O0

UFOA0 = 01

LETn_O1

UFOA0 = 10

Pulse Seq. 1

REP0IF

REP0IF

Pulse Seq. 2

REP0IF

Pulse Seq. 3

The first two sequences are loaded into the LETIMER before the timer is started.

LETIMERn_COMP0 is set to 2 (cycles – 1), and LETIMERn_REP0 is set to 3 for the first sequence, and

the second sequence is loaded into the buffer registers, i.e. COMP1 is set to 1 and LETIMERn_REP1

is set to 4.

The LETIMER is set to trigger an interrupt when LETIMERn_REP0 is done by setting REP0 in

LETIMERn_IEN. This interrupt is a good place to update the values of the buffers. Last but not least

REPMODE in LETIMERn_CTRL is set to buffered mode, and the timer is started.

In the interrupt routine the buffers are updated with the values for the third sequence. If this had not been

done, the timer would have stopped after the second sequence.

The final result is shown in Figure 21.10 (p. 297) . The pulse output is grouped to show which sequence

generated which output. Toggle output is also shown in the figure. Note that the toggle output is not

aligned with the pulse outputs.

Note

2011-04-12 - d0001_Rev1.10

297

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