Are two channels of RS-485?

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vali_ile
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Are two channels of RS-485?

Post by vali_ile » Mon Feb 10, 2020 7:19 pm

Hi, Ivan

There are two channels of RS-485 in Modbus RTU in drawing cnc42.com/_media/hardware/et10/et10-uart-001.png.
How to address any one of them separatelly by a PLC procedure?

Because

I want to use one channel for communication to my VFD as defined in http://docs.pv-automation.com/mycnc/myc ... 1424c3b_46
But in http://docs.pv-automation.com/mycnc/modbus_setup you explicitly stipulate that "NOTE: In order for the Modbus device to connect properly, the "RS485/Modbus communication" checkbox should be UNCHECKED in the Config > Technology > Mill/Lathe > Spindle configuration dialog".
So, apparently, there is a conflict somewhere or I don't understand how it works.

----
And I want to use the other channel for communication with other RS-485 Modbus modules.

In this case, one would be Master for one network and the other one Master for a different network.

Still, I want to write procedure in PLC to address any Master I'd like to use.

So, what is the right procedure to implement and use both channels of Modbus RTU integrated in myCNC Controller ET10?

***
A second matter related to the clarity in documentation - in http://docs.pv-automation.com/mycnc/modbus_setup you speak about virtual ports, but there is no further explanations about what do you mean - ports, virtual port not assign to physical port, etc.

***
P.S. As a side note, it would have been nice to have at least on one channel the possibility to use 4 wire connection instead of having them internally connecte for 2 wire connection (as specified in http://www.modbus.org/docs/Modbus_over_ ... _V1_02.pdf).
I know that for some customer could have been confused to set one more jumper to switch from 4 wire to 2 wire, but still...

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vali_ile
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Re: Are two channels of RS-485?

Post by vali_ile » Mon Feb 10, 2020 7:31 pm

Also,

Would you, please, check for me if in the image for Modbus RTU http://cnc42.com/_media/hardware/et10/et10-uart-001.png the connector specifications are correct or are they as in the connector I've redraw in attachment ?
RS485 corrected myCNC connector.jpg
You said " A is +, B is -" for RS485 and from internal diagram I presumed that internal RS485_0_A should be pin RS485 #1 A.
Or are they inverted?

I'm puzzled! :?

ivan
Posts: 233
Joined: Tue Apr 16, 2019 5:30 pm
Location: Ottawa, Canada

Re: Are two channels of RS-485?

Post by ivan » Mon Feb 10, 2020 8:43 pm

1) Regarding the two channels - channel #0 is reserved for special purpose projects (Hypertherm interface, capacitive height sensor, IPG laser). For most clients, one Modbus master is enough, since multiple devices can be controlled through one Modbus channel. So out of box, only one Modbus channel is available for you to program through PLC (channel #1).

2) I have edited the wiki page to explain how our Modbus setup works. Effectively, you can have low-level access, where you program all Modbus communication through PLCs (very hands-on), or high-level access, where you simply set the parameters for the VFD in the Spindle settings window. If using the high-level access, the check mark next to RS485/Modbus communication should be set to ON, and if using low-level communication, the check mark should be set to OFF. We will rename this setting in the software to better reflect what's happening in one of the upcoming releases.

3) Virtual ports are ports that can be assigned in the myCNC software, but don't actually have a physical hardware equivalent on the board. So the software thinks there is a port, while in reality no hardware port is actually present (for example, there is an input port #70 in the Diagnostics window, while the ET10 board only has 48 inputs). This allows us to use those reserved software ports when effectively expanding the number of I/O ports of the board while using Modbus.

4) We have double-checked, and the diagram on our wiki seems to be correct. A is indeed +, B is indeed -, and channels #0 and #1 seem to be labelled correctly.

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vali_ile
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Re: Are two channels of RS-485?

Post by vali_ile » Mon Feb 10, 2020 9:11 pm

Thank you, Ivan, for swift answer.

But at point 4), I disagree with you - what I meant is

Following the internal schematic presented in the left side (where DD16 is noted as channel #0 and DD22 as channel #1 ) doesn't match with labels on the right side of the picture (where RS485_0_A is connected to pin 4 labeled as RS485 #1 A, idem for the pins, 2, 3 and 5) and this is the reason to post that initial attachement.

ivan
Posts: 233
Joined: Tue Apr 16, 2019 5:30 pm
Location: Ottawa, Canada

Re: Are two channels of RS-485?

Post by ivan » Wed Feb 12, 2020 3:20 pm

I see what you're asking now. The labels on the right hand side of the picture are correct in labeling channels #0 and #1. The internal schematics are for internal reference only, so they use a separate numbering system which does not always correlate to how we label our boards.

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