Connecting VFD to Rs-422 on mesa7i76e

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27 Sep 2022 13:54 #252858 by webutt
I have two VFDs connected to the Rs422 interface of mesa 7i76e, controlling two servo motors. I am able to setup linuxCNC with the mesa card but I can't find any resources on how to control the VFDs via 7i76e's 422 interface.

VFD: MR-J2SA

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29 Sep 2022 14:54 #253032 by HansU
RS-422 is only the electrical interface and I guess you will run Modbus over RS-422?

I can point you at least to this as a general example how to use Mesa's UART: linuxcnc.org/docs/2.9/html/man/man9/mesa_uart.9.html

If you want to use Modbus, here a hint, that the PktUART is the best choice:
forum.linuxcnc.org/10-advanced-configura...-uart-for-modbus-rtu

So maybe these are of interest:
linuxcnc.org/docs/html/man/man3/hm2_pktuart_setup.3hm2.html
linuxcnc.org/docs/html/man/man3/hm2_pktuart_read.3hm2.html
linuxcnc.org/docs/html/man/man3/hm2_pktuart_send.3hm2.html

 

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29 Sep 2022 16:09 #253033 by flawapawacrew
Hello, manual page 296 seems to explain the communication protocol pretty clearly. You might be able to make it work with mesa_uart (although not easily).

Do you want to control the servo position (or velocity) in real-time? Then I do not think that the RS-422 interface is meant for this. The list of commands on pages 304-307 only show position commands in "test operation mode" (p. 315), which is most likely not suited for real-time control.

The absolute expert on mitsubishi servos here on the forum is dm17ry. He explains that the RS-422 interface is not meant for real-time control here: forum.linuxcnc.org/27-driver-boards/4557...e-7i94-config#239795

Cheers,

flawa

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