How does a computer trasmit Gcode?

[JJDennon]

I am interested in writing my own CNC control program. How does the computer actually transmit the gcode? I assume one line of gcode is transmitted at a time and there must be some kind of response by the hardware-based interpreter giving the go-ahead to continue on.

Can someone point me towards a communications spec?

1. Open parallel port
2. ??

[Andre' B]

That is going depend on the "hardware-based interpreter".
You need to pick one and read the programming manual and have a chat with the manufacture of the unit.
Any decent unit would come with souce code samples and a library of functions to make things easier.

[JJDennon]

That is going depend on the "hardware-based interpreter".
You need to pick one and read the programming manual and have a chat with the manufacture of the unit.
Any decent unit would come with souce code samples and a library of functions to make things easier.

How does a program like Mach3 work then? Mach3 can talk to a number of different drives, and you just provide it an XML configuration file about your drive and that tells it how to talk to the drive.

Surely there has to be general purpose guidelines for this. This stuff has been around since the 70s!

[Al_The_Man]

This stuff has been around since the 70s!

But in different formats and methods, the original commercial systems used (uses) all in one proprietary co-processors for the HMI, CNC & PLC controllers.
Then came the PC based Motion cards such as Delta-Tau, Galil and Acroloop and the PC just provided the HMI, the cards closed the motion loop the same way the commercial systems do.
The method Mach uses is an HMI that also calculates the machine trajectory, this is then passed over to the motion drives via the P.P. Mach then relies on the stepper or in the case of servo's closed loop drives to complete the move.
IOW, there is no feedback to Mach (non-closed loop).
Al.

[JJDennon]

So what does Mach actually transmit to the drive then? It's it gcode or some modified, compiled thing?

The method Mach uses is an HMI that also calculates the machine trajectory, this is then passed over to the motion drives via the P.P. Mach then relies on the stepper or in the case of servo's closed loop drives to complete the move.
IOW, there is no feedback to Mach (non-closed loop).
Al.

[Bubba]

Basically, Mach sends a timed data string of pulses for step and direction out the parallel port. Nothing more, nothing less. All of the computation to covert G-code to timed pulses is done in the computer.

[ger21]

and you just provide it an XML configuration file about your drive and that tells it how to talk to the drive.

All the .xml file does is contain the Mach3 configuration. All it really does is tell mach3 which pins to send the step and direction signals.

If you want to know more about how Mach3 works, download the plugin SDK.

[JJDennon]

All the .xml file does is contain the Mach3 configuration. All it really does is tell mach3 which pins to send the step and direction signals.

If you want to know more about how Mach3 works, download the plugin SDK.

Great idea, should give me a better understanding on that. There is also EMC2 as well.

[ger21]

How does the computer actually transmit the gcode? I assume one line of gcode is transmitted at a time and there must be some kind of response by the hardware-based interpreter giving the go-ahead to continue on.

What Mach3 does (when used with the parallel port), is take control of the PC to get very precise timing. It then calculates the required step and direction signals, and places them in a buffer, sending them out in the correct time slice. There is no response with the go ahead, the signals are sent at the pre-determined time. What Mach3 does is extremely complex, and it took Art (the author) years to get it where it is now.

[TarHeelTom]

I am interested in writing my own CNC control program.

My question is WHY? What do you hope to achieve which can't be done with the two fine machine controllers on the market today, Mach3 and EMC2? What features do you plan to add?

The US Government spent several million dollars developing EMC, and it was no great shakes.

Then a handful of independent programmers took over the program and spent years and untold (and unpaid) thousands of man-hours turning it into the product it is today (EMC2). It's a robust product which will run all sorts of different machinery with as many as 9 different axes. And at least 8 programmers still spend a lot of time trying to improve different functions and keep EMC2 up-to-date. Al has already mentioned the blood, sweat, and tears which Art has poured into Mach3.

I don't pretend to be a brain surgeon, but consider the many functions required to run just a single line of G-code. A single line might request a cutting move with 5 axis of movement. The controller has to calculate all the geometry to the moves, and keep the cutter moving at a constant rate along the material, (which will frequently involve changing the speed of each different axis drastically). A rapid move, for example, requires not only the calculations to accelerate each axis up to speed, but needs to frequently calculate the distance left for the move and then calculate the amount of deceleration required to slow the move as to not overrun the move end points.

Tom

[JJDennon]

My question is why not?

I've done some work professionally developing front ends for Fanuc and Seimens controls, and it was pretty fun work. I had the opportunity to really re-think the UI and make some improvements. The response from the machine operators and programmers was pretty positive compared to the software they were using before. The Mach3 UI is pretty archaic and rough on the eyes, the same with EMC2.

Really there is more work here than I want to take on at this point in time, but the end result would be software that would be enjoyable to use.

My question is WHY? What do you hope to achieve which can't be done with the two fine machine controllers on the market today, Mach3 and EMC2? What features do you plan to add?

Tom

[ger21]

The Mach3 UI is pretty archaic and rough on the eyes, the same with EMC2.

It's much easier to create a Mach3 screen, then create a new mach3.

Here's two that I've done.

The CNC Woodworker - Mach3