7i97T - Custom bitfile request (High-speed 200MHz Encoder for Linear Motors)

I would try setting:

hm2_7i97.0.encoder.muxed-sample-frequency

to say 20 MHz

(you can probably go higher by futzing with the muxed- skew parameter)
 

Hi PCW,

Thank you so much for the incredibly fast reply!

I will add setp hm2_7i97.0.encoder.muxed-sample-frequency 20000000 to my HAL file right away and test the machine.

Just to make sure I fully understand the limits of the hardware: what are the acceptable or maximum values for this parameter with the standard 7i97T bitfile? For example, does it need to be a specific integer divisor of the base clock? Also, at what frequency would I typically need to start adjusting the muxed-skew parameter you mentioned?

Thanks again for your time and excellent support!

Gotrune wrote:

[code][code]my high-resolution optical scales (...) are dropping pulses during high acceleration

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Acceleration has nothing to do with it.
Only maximum speed matters.
From the resolution and speed you will calculate the pulse frequency.

Oh, yes I understand,
Thx

20 or 25 MHz (2.4x or 3x faster than the default 8.3333 MHz), works fine with no skew added.
I would be comfortable with those settings.

The frequency value you set will be rounded to the closest available frequency
= an integer division of the 100 Mhz FPGA ClockLow. This is easy to test with halshow.

As you go faster, the timing margins become smaller and you must adjust to the delay in
the actual hardware multiplexing with the skew adjust (in ns) but at the higher speeds
the timing variations over voltage and temperature limit the practical maximum.

That is, I can get all encoders to work with a 50 MHz mux rate (and 20 ns skew) but I would not trust
it without doing at least a temperature cycle.

Timing errors will show up as even/odd encoder swaps or crossover between even/odd encoders
so don't experiment on a powered servo system...