Modbus input for absolute encoder position?

Thanks Andy.

Still learning LinuxCNC - so I might ask stupid questions.

I set up LinuxCNC in closed loop (velocity mode). The incremental encoders are driving the PID for the axis. That is working fine.

The ModBus reading would be too slow to drive the PID.

Does your example this still apply?

Regards,
Markus

0x2102 wrote: The ModBus reading would be too slow to drive the PID.

The PID updates once per mS. Modbus can transfer hundreds of registers in that time.
But I think that you are correct, in that both modbus2hal and Classic Ladder modbus implementations run in user space.

What is the actual servo drive?

Does your example this still apply?

With modifications, probably. You would need to add together all three numbers (incremental encoder counter float position, mutli-turn and single turn)
That would need two sum2 components per axis, or you could make a simple HAL component as a 3-way adder with scaling / number conversion. This might be needed if the modbus register are likely to change during operation, you would want to latch the initial numbers if you are also using the incrmental output.

They are JMC 400W Servos with a JASD4002-20B drive.

www.jmc-motor.com/product/903.html

www.jmc-motor.com/file/1806085008.pdf

I guess it would be a nice to have feature, but it's not really that critical.

What interface hardware are you using? Maybe you can be the first to do realtime modbus with a Mesa UART.

I do have a couple

Currently I have a 7i95 on my test bench that I planned on using for this setup.

I also have a 7i76e and 7i92+7i76+7i77 available.

That would interest me, too. I'll read along.

greeting Siggi