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Parallel port not recommended???
« on: February 04, 2017, 08:27:48 AM »
I ordered and recieved my g540 motion controller and was ready to purchase a mach4 hobby and legacy port plug-in when I stumbled across the following blurb....

"We do not recommend using the parallel port with Mach4 as performance is reduced by both this data connection and the processing and memory power of older computers."

The machine I would use would be either a win xp or win 7 refurbished with 4gb of memory and integrated video.  Is this even going to work in light of the statement above???

Offline Tweakie.CNC

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Re: Parallel port not recommended???
« Reply #1 on: February 04, 2017, 08:42:38 AM »
I have both the parallel port plugin and an ESS motion controller working with WinXP & Mach4. Overall, the performance is a lot better when using the ESS.
My recommendation - go for a motion controller.

Mach4 is quite heavy on graphics so try your integrated video but be prepared to add a graphics card if necessary.

Tweakie.
« Last Edit: February 04, 2017, 08:45:27 AM by Tweakie.CNC »
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Re: Parallel port not recommended???
« Reply #2 on: February 04, 2017, 09:36:49 AM »
Well, I am now on the gecko g540 path after buying it.  I had looked at the ESS, but the coin was tossed and I ended up going form g540 instead.  You say you have pp and ess, but I thought the ess didn't need the pp plug in.  What am I missing?
 

Offline Tweakie.CNC

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Re: Parallel port not recommended???
« Reply #3 on: February 04, 2017, 10:23:33 AM »
You still need a motion controller (or the PP plugin) to operate your G540.  ;)

Perhaps I didn't explain it correctly - I have both the PP plugin and the ESS and comparatively the ESS is better.

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.
Re: Parallel port not recommended???
« Reply #4 on: February 04, 2017, 11:08:46 AM »
So, you have Mach4 on the computer (os??).  A parallel cable that connects the computer to the ESS.  You don't use the Ethernet cable from the computer to the ESS?

Not really trying to pepper you with questions, but I have found it difficult to get my head wrapped around this.  I have been using chilipepr and tinyg and am not entirely happy with that arrangement, thus the purchase of the g540.

Have you used the gecko g540 to give you a point of comparison between the ESS and the g540?  (obviously, now that I have plunked down the money for the g540, I wan't to find a very good reason not to use it if I don't)

Re: Parallel port not recommended???
« Reply #5 on: February 04, 2017, 11:42:48 AM »
You still need a motion controller (or the PP plugin) to operate your G540.  ;)

The g540 IS the motion controller, right?  I was thinking I just need to connect the g540 to the computer running Mach4 and the legacy parrellel port plug in via a pp cable.   Is that a correct plan or am I still not getting it?  Is there a disadvantage doing it that way?
« Last Edit: February 04, 2017, 11:45:06 AM by crchisholm »
Re: Parallel port not recommended???
« Reply #6 on: February 04, 2017, 02:45:54 PM »
Hi crchisholm,
you are correct, a Mach4 licence and a Darwin Parallel Port licence and you are ready to go.

The pulse streams required to activate your stepper drivers (in the 540) are generated by your PC when using a parallel
port. The computer does this by running a timer where it resets a counter and when it counts up to a certain number it generates
an interrupt and the program resets the counter and starts again and also issues a pulse to the parallel port. The timers available
in a PC CPU chip are pretty limited by comparison to microcontrollers suitable for controlling machinery. Microcontrollers have hardware
timers that count up, reset and issue a pulse without CPU intervention. A PC timer requires considerable CPU processing to issue a
pulse stream and are generally called 'interrupt driven' timers.

The downside is that PC CPUs use interrupts for lots of different purposes, a simple one is the realtime clock, it generates an interrupt every
100ms or so just so it can keep the clock on your screen updated. It also uses them to switch between different software threads which we expect
to run at the same time. If two or more interrupts happen at once one will have to be delayed while the other one is processed. As far as our
pulse stream goes it means one pulse is 'late'. This variance in pulse timing is a fact of life with a parallel port and is called 'timing jitter'. There
is a test program which tries to measure jitter and therefore establish if or how well a parallel port will operate.

Some PCs do a good job of running a parallel port with low jitter and some do not. Very powerful and capable PCs are not necessarily any better
than an old XP clunker. Laptops generally do a poor job. Some PCs can be improved by turning certain things off and disabling certain automatic
features. In most cases you cant have different programs running with Mach as one program will interfere with Mach and the regular pulse stream
is broken. The good news is that many PCs do work OK and tens of thousands of CNCers around the world still use the parallel port.

For PCs that wont run a parallel port or if you require very stable pulse streams thats where external motion controllers come into play. They have onboard
either or both an FGPA and a microcontroller which generate very high quality pulse streams and very very much faster pulse streams than can be generated
by a PC alone. The result is smoother motion and also means that the pulse stream can 'keep up' with highly precise servo encoders for which a PC cant.

I suggest you use a parallel port, its a good fit with your existing machine and at a later date add an external controller if you think it desirable.

Craig
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Offline ger21

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Re: Parallel port not recommended???
« Reply #7 on: February 04, 2017, 04:46:40 PM »

The g540 IS the motion controller, right?  I was thinking I just need to connect the g540 to the computer running Mach4 and the legacy parrellel port plug in via a pp cable.

No, the G540 is a stepper drive.
In your case, the parallel port is the motion controller. But what Tweakie is saying, is that an external motion controller is highly recommended. The ESS is an Ethernet Smooth Stepper.
Gerry

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Re: Parallel port not recommended???
« Reply #8 on: February 04, 2017, 06:52:36 PM »
yeah, the terms are what get me in trouble.   I will probably end up getting the ESS, but I want to buy it when I have a particular problem to solve (fortunately, I am not doing this for a living).  I have a long history of jumping the gun because I just knew I had to have this thing that is now sitting amoung a lot of other things in my think closet.

So in that case I would be connecting the computer to the ESS via a cat5 cable and then the Ess would use a a pp cable to go  to the g540, right?

Re: Parallel port not recommended???
« Reply #9 on: February 04, 2017, 06:56:12 PM »
Thank you joeaverage.  That was a very useful explanation of the process (and also a good illistration of why I will probably end up getting the ESS.