problem with qep on tms320f2812 dsp

hi all!
i am trying to interface an encoder with the QEP hardware in ti dsp 2812
but the bahaviour of the QEP hardware does not seem to be consistent.
sometimes i get the encoder pulse counts in 'T2CNT' register but most of
the times 'T2CNT' shows all zeroes.i get proper pulses from the incremental
encoder which i give to the 2 QEP input pins.what could be the problem?
please help.

thanks
mit.

On Sat, 06 Sep 2008 06:41:19 -0500, mit wrote:

> hi all!
> i am trying to interface an encoder with the QEP hardware in ti dsp 2812
> but the bahaviour of the QEP hardware does not seem to be consistent.
> sometimes i get the encoder pulse counts in 'T2CNT' register but most of
> the times 'T2CNT' shows all zeroes.i get proper pulses from the
> incremental encoder which i give to the 2 QEP input pins.what could be
> the problem? please help.
>
> thanks
> mit.

Are your logic levels correct? They're going high enough and low
enough? Check the specifications for the processor, to make sure that
you're meeting its needs.

Does the problem seem to be speed dependent? If so, you may either be
clocking the QEP module too slowly, or your voltage levels may be speed
dependent (they often are). If they're marginal at low speeds, chances
are they're just wrong at high speeds.

Have you figured out _when_ the thing works and _when_ it doesn't? With
intermittent problems, finding the "switch" that you can flip to make it
consistently fail or succeed is like finding the holy grail -- nothing
puts you on the path to diagnosing the problem quicker than that.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html

Hi!
thank you for replying.i am using a texas instruments dsp TMS320F2812
whose input pin voltage levels are 0 to 3.3V . i checked the voltage levels
of the encoder pulses which are also 3.3v so they match exactly with the
processor's specifications.
The voltage levels are not speed dependent either.
The dsp datasheet says that the QEP input frequency should be less than or
equal to 1/4th of the device frequency( i am using 150Mhz) and the QEP
input frequencies i am getting are in the range of khz(less than 1/4th of
150Mhz).
The qep clock is generated internally which is 4 times the QEP input pulse
frequency so i think the QEP module should work with any clock frequency,
even really low ones.
Even if i increase the QEP clock frequency i am not getting any results.
i'll be grateful if you can give any more suggestions.

thanks a lot.
mit


>On Sat, 06 Sep 2008 06:41:19 -0500, mit wrote:
>
>> hi all!
>> i am trying to interface an encoder with the QEP hardware in ti dsp
2812
>> but the bahaviour of the QEP hardware does not seem to be consistent.
>> sometimes i get the encoder pulse counts in 'T2CNT' register but most
of
>> the times 'T2CNT' shows all zeroes.i get proper pulses from the
>> incremental encoder which i give to the 2 QEP input pins.what could be
>> the problem? please help.
>>
>> thanks
>> mit.
>
>Are your logic levels correct? They're going high enough and low
>enough? Check the specifications for the processor, to make sure that
>you're meeting its needs.
>
>Does the problem seem to be speed dependent? If so, you may either be
>clocking the QEP module too slowly, or your voltage levels may be speed
>dependent (they often are). If they're marginal at low speeds, chances
>are they're just wrong at high speeds.
>
>Have you figured out _when_ the thing works and _when_ it doesn't? With

>intermittent problems, finding the "switch" that you can flip to make it

>consistently fail or succeed is like finding the holy grail -- nothing
>puts you on the path to diagnosing the problem quicker than that.
>
>--
>
>Tim Wescott
>Wescott Design Services
>http://www.wescottdesign.com
>
>Do you need to implement control loops in software?
>"Applied Control Theory for Embedded Systems" gives you just what it
says.
>See details at http://www.wescottdesign.com/actfes/actfes.html
>