Modbus input for absolute encoder position?

0x2102 wrote:

Multiturn Count: 0 - 65536
Pulses per Turn: 0 - 65536

I was wondering if anybody was able to get this to work in LCNC as PCW/andypugh described? ModBus absolute position read at startup and then incremental encoders for realtime feedback.

I think it might be simpler than you think. You should be able to just add the numbers together in HAL and use directly.

Note that the sum2 HAL component has separate gains for the two inputs, so you can scale one for distance-per-turn and the other for distance-per-pulse.
You might need to convert from signed integer (S32) to Floating point, but that, plus specifying absolute encoder homing should be all that you need.
(This assumes you are reading the Modbus in a realtime thread, of course)

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.

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

So, do you know the register numbers that contain the data? (and thus the modbus transaction data)

You should, I think, be able to connect all the drives to one serial port, including the one on the 7i76e.

I think it might be relatively easy to write a .comp that loads like:
[/code]loadrt mesa_modbus uart="hm2_7i76.0.uart.0" addr="151,151,152", regs="55,65"[/code]

It might be better to have something like the format used for absolute encoders :
ssi_chan_0=error%1bposition%24g
Possibly using all the same code, in fact.

This is one existing implementation of a driver for the Mesa UART:
github.com/LinuxCNC/linuxcnc/blob/master...ivers/mesa_uart.comp