Hello,
About Spindle Setup Special Funtions with PWM Control:
1.- 
Reading the manual 5.3.6.7 Special Functionm say:
"Use Spindle feedback in sync mode should be unchecked."
That's all, nothing more.
So I can not understand the purpose of that function,
I would like to know about this
2.- 
About "sync mode"
look for this, and did not find.
I can not understand the sync mode, 
I need a glossary with Mach3 terminology
I would like to know about.
3.-
About Special Function: "Closed Loop Spindle Control"
I seek to know the frequency, the time between each pwm update.
how often the pwm is updated?
How do I calculate the time (frequency) of PWM updates ?
I would like to know about.
4.- 
Reading this forum, I found something opposite:
http://www.cjh.com.au/PWM%20Spindle%20Control%20using%20Mach3.pdfSay:
"Do not use Closed Loop Spindle Control. 
Selecting “Use Spindle Feedback in Sync Modes” tells Mach3 to expect feedback pulses from the spindle. 
Selecting this effectively puts Mach3 into a closed loop mode."
Thank related information. 
I appreciate your time and attention.