Encoder support in NI Lab View

[Lafleur]

We have some question related to shaft encode support...

the reference below states that we can use 4 encoder at 4x speed:
what is 4x and 2x relate too.. How fast the encode can turn with out the cRio missing a count? what is the max rate in 4x, 2x and 1x??

Is it 4 channel of quadrature A and B using 8 digital in, allowing for 4 encoders, or is it 4 digital in supporting only 2 encoders?

from FRC user guide:

"The FPGA on the CompactRIO device contains four quadrature decoders
that perform 4x decoding and eight decoders that perform 1x and
2x decoding to interpret the information the encoders return. The decoders
are not tied to a specific module or channel on the CompactRIO device.
You can reserve and release decoders as needed."


tom lafleur
mentor team 812

[rfolea]

Normally, you would get a single increment in your counter for every A/B Cycle (A goes high, then B goes high).

4X encoding means you get 4 increments for each cycle (one for the rising edge of A, another for the falling edge of A, another for the Rising edge of B, another for the falling edge of B).

So ... if you have a 128 count encoder, it will act like a 128x4 = 512 count encoder!

This increases the resolution of your encoder by 4x for free.

The 2X gives you two increments per cycle.