Problem in creating waveforms with the help of timer

[sanjib]

Posted on April 29, 2014 at 11:44

Hi All

The waveform.png file I have attached to show what i have to do. I have to generate similar kind of waveform with using one timer . The timer clock is 168 MHz...... One waveform will be 2 clock on and 4 clock off again 2 clock on , 4 clock off so on for 5 micro sec like wise the other one bur in the opposite way . there should be 1 clock cycles delay between waveform 1 falling edge and waveform 2 rising edge and vice versa.

Is this possible to do .. if yes can any body guide me how to achieve this

[sanjib]

Posted on April 29, 2014 at 11:59

Sorry Please find the attachment to see the waveform. I have attached the waveform

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Attachments :

waveform.png : https://st--c.eu10.content.force.com/sfc/dist/version/download/?oid=00Db0000000YtG6&ids=0680X000006Hzst&d=%2Fa%2F0X0000000bR0%2F5Ji2bnTMJR_hX542tr0oGe8LOwfRYFp2H7TAEIrNLUI&asPdf=false

[chen]

Posted on April 29, 2014 at 13:47

Hi

''Is this possible to do .. if yes can any body guide me how to achieve this''

Yes.

Since you want 2 different waveforms - you will need 2 timers.

You can slave 1 timer to another, the slave will start synchronously with the first.

The waveform you want is not square - so you cannot use simple timer (toggling IO will give a square wave).

Instead, you will have to use PWM mode, this will involve a CCMRx register for each timer.

The ARR reg controls the period of the PWM.

The CCMR reg cotnrols the pulse width.

[sanjib]

Posted on April 29, 2014 at 14:32

Sorry it is not 2 clocks it is 280 clocks  and 1 clocks is 140 clocks and 4 clocks is 420 ....Do you have any example for that

[sanjib]

Posted on April 29, 2014 at 14:34

but I should use 2 different channels of 1 timer not 2 timer is that possible

[chen]

Posted on April 29, 2014 at 17:29

''Do I have any examples''

No.

Search the STM32 forum. Clive1 has provided PWM examples.

I think it is a simple case of copying the same code for 2nd timer and then slaving it to the first (I have not done it myself).

''should use 2 different channels of 1 timer not 2 timer is that possible''

No.

2 Timers and 2 channels. The timers provide the count. The channels provide the capture/compare register (CCMRx).

[sanjib]

Posted on April 30, 2014 at 07:28

but how it is possible to get a delay of 140 clocks between those waves , when will start synchronously

[chen]

Posted on April 30, 2014 at 11:27

Hi

Basic Timer operation.

Timer is just a counter.

Timer has various clocking schemes - clocking mean incrementing/decrementing count CNT - counting frequency.

Timer has register to count up to, then will reset (back to 0) - ARR -known as period.

Timer can be connected to IO pin (do not have to use ISR to toggle IO pin - done automatically)

This is basic mode.

Timer has more advanced modes - 1 of them is PWM output.

PWM uses 'channel' - uses the CCMRx register

The CCMRx register controls Duty Cycle - ratio of on/off

eg

ARR = 100

CCMR = 50

50 % Duty cycle

ARR = 100

CCMR = 25

25 % on, 75% off

Timer Advanced mode - can link (slave) one timer to another.

All slave timers will be reset (CNT = 0) by master timer