TMC423 Encoder position register

[krunal_299]

According to the 423 datasheet, i don't get myself cleared how the contents of encoder position register going to be changed on reading the encoder pulses.
Does this position reg. incremented/decremented by 1 either on each compelete pulse of channel A or on every transition of the pulse?
More explicitly, with initial value of 000hex in Encoder position reg. and prescalar set to 1.6, what will be the data this reg have after detecting 400 pulses on channel A from relevant encoder?(calculate for 1000 PPR encoder and 6400 microstep).
With waiting 4 your reply.

[TRINAMIC_BD]

The TMC-423 counts up / down with every encoder step, using quadrature evalution of the encoder signal, i.e. a 1024 line encoder give 4096 counts per rotation. When you use the scaling function, it counts up / down by a value which is given by the pre-scaler factor.
When you do not find a fitting pre-scaler factor for your system requirements, it is most universal to work with a factor of 1, and do a scaling later on in software.

[krunal_299]

ok Thank you very much !
so with following example:

with initial value of 000hex in Encoder position reg. and prescalar set to 1.6, what will be the data this reg have after detecting 400 pulses on channel A from relevant encoder?(calculate for 1000 PPR encoder and 6400 microstep).

The data of position reg. is= 190hex(400 dec)
am i right?
if yes then with proper prescalar factor we get the exact no. of microsteps of motor in position reg. ok?
let it be cleared to me.

[TRINAMIC_BD]

400 pulses on channel A means 400*4=1600 encoder steps, because it also means 400 pulses on channel B, i.e. each 800 transitions. The position counter thus counts 1600*pre_scaler=1600*1.6=2560.

For the 1000 PPR encoder and 6400 microstep, you need a pre-scaler of 6400 / (4*1000)=1.6.

[Andrew]

I am not sure what exactly you are trying to adjust the prescaler for, and what is your perception of what you might achieve.
I just would note that an encoder does not count steps. It indicates position.
Position is not rock solid.
Microsteps are not rock solid either.
There will always be deviation.

Trinamic Motion Control Language (TMCL) has a parameter for deviation, and how to treat deviation. Which exactly these parameters are depends on the model of a module. Although I think that they must be unified across all models, especially that now all modules can attach to an encoder.
This note is a general one.
Of course you are talking about a chip, rather than a module. Still you might want to mimic the behaviour of TMCL in your circuit board. Yet you do use an Evaluation board, which has TMCL on board.

For postion related articles you may want to read starting from here:
http://www.trinamic.com/ttdg/viewtopic.php?t=469

[krunal_299]

Thnx for such a QUICK response!
so from this discussion, i conclude the following statement for encoder relating caculation within the 423:

With proper prescalar factor setting, the encoder position register represents the no. of microsteps motor has taken.
pls let me know anything i misunderstood by this conclusion.
With Warm Regrads!

[TRINAMIC_BD]

Exactly! We have just again updated the TMC423 documentation, to better explain the meaning of the pre-scaler factor bits.

With best regards,
Bernhard

[Andrew]

the encoder position register represents the no. of microsteps motor has taken

I think this is wrong. You both ignored my note:

an encoder does not count steps. It indicates position.

Please note, that Bernhard meant steps of encoder. Not steps of a motor.

Physically encoder cannot count steps.
Controller does count steps. - Not encoder.

In order for a measurement device to count steps of another device - a motor - the measurement device needs to be super smart, so that it discerns between a step, and an ambient deviation.