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Unread 04-04-2009, 14:55
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Re: Victor Vs Jaguar

Quote:
Originally Posted by EricVanWyk View Post
Bill -

Alan's post is only half correct. It is true that the outputs have a 6.625uS update rate, which does equate to 150 signals over the standard window.

However, this is slightly higher resolution than the Victors can respond to. Additionally, the Jaguar does not use the standard 1ms - 2ms window by default (it can be set to do so). It uses a wider window in order to get more resolution. This is why you must use the Jaguar or Victor specific API calls - they will scale the pulse width accordingly.

I don't have access to the exact numbers right now - I've managed to get out of the office this weekend. Hopefully someone with better knowledge of the specifics will jump in.

I'm 30% confident that internally, the Jaguars represent the Duty cycle with a 16 bit number (even though they are using a 32 bit processor). I'd be surprised if we are getting more than 8bits over the PWM channel, so this extra resolution isn't used (this year).

Honestly, having a ~150 Hz update rate has no relevance to the answer I am looking for, but in regard to the OP's question, it might. I understand the Vic and the Jag have different update rates and their responses to the signals are significantly different. For instance, the Jag has a much more linear response than does the Vic. All this aside, what I was really looking for was:

While doing the math to generate the values used to send to the Jag, how many decimal places are really necessary? Would sending .38 have any noticeably different output than sending it .3835?

If in fact the Jag is using a 16 bit word to represent the duty cycle, that would translate to more than 65K possible values. That would indicate that 4 places would in fact work, though I highly doubt that you would really need more than 2 places after the decimal.

All this may be limited by the cRIO at this point in time. While sending a PWM signal generated by these values, the cRIO may only be looking at the first two digits and ignoring the rest. This is just a guess on my part. When we move to CAN Bus, this whole discussion will be somewhat different, but that is for the future.
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