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Jérôme
Jérôme
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I got help from someone more knowledgeable on the matter and got isit sorted out. There were a few issues.

Here's a few pieces of information I would have been happy to find somewhere on the Internet when I was stuck.

In the waveshareWaveshare configuration UI, there is a "Multi-Host Settings" section. I have no idea what multi-host means so I left if untouched. It appears I needed to set Protocol to "Modbus TCP to RTU". Might sound obvious, but due to the name of the section, I didn't even try anything there. I guess on my earlier working setup I touched everything and had this right.

More importantly, while the Tx-/Tx+ convention is universal, the A/B seems not to be, and it appears Waveshare and Schneider don't agree on which is A and which is B. So I got the wiring switched the wrong way. Some Schneider docs only show A/B which makes it even worse. Beware of A/B, only trust Tx-/Tx+. I did try to switch the wires but due to the other error it wouldn't work either.

My setup worked until I added devices to the bus. When I did that, I had to rewire the whole bus and this is probably when I switched Tx+/- the wrong way due to the A/B ambiguity.

I also learnt in the process that some gateways and devices support 4-wire Modbus. I tried a Teltonika gateway that has Rx+/Rx-/Tx+/Tx- pins and it wouldn't work until I connected Tx- and Rx-, and Tx+ and Rx+ together.

I got help from someone more knowledgeable on the matter and got is sorted out. There were a few issues.

Here's a few pieces of information I would have been happy to find somewhere on the Internet when I was stuck.

In the waveshare configuration UI, there is a "Multi-Host Settings" section. I have no idea what multi-host means so I left if untouched. It appears I needed to set Protocol to "Modbus TCP to RTU". Might sound obvious, but due to the name of the section, I didn't even try anything there. I guess on my earlier working setup I touched everything and had this right.

More importantly, while the Tx-/Tx+ convention is universal, the A/B seems not to be, and it appears Waveshare and Schneider don't agree on which is A and which is B. So I got the wiring switched the wrong way. Some Schneider docs only show A/B which makes it even worse. Beware of A/B, only trust Tx-/Tx+. I did try to switch the wires but due to the other error it wouldn't work either.

My setup worked until I added devices to the bus. When I did that, I had to rewire the whole bus and this is probably when I switched Tx+/- the wrong due to the A/B ambiguity.

I also learnt in the process that some gateways and devices support 4-wire Modbus. I tried a Teltonika gateway that has Rx+/Rx-/Tx+/Tx- pins and it wouldn't work until I connected Tx- and Rx-, and Tx+ and Rx+ together.

I got help from someone more knowledgeable on the matter and got it sorted out. There were a few issues.

Here's a few pieces of information I would have been happy to find somewhere on the Internet when I was stuck.

In the Waveshare configuration UI, there is a "Multi-Host Settings" section. I have no idea what multi-host means so I left if untouched. It appears I needed to set Protocol to "Modbus TCP to RTU". Might sound obvious, but due to the name of the section, I didn't even try anything there. I guess on my earlier working setup I touched everything and had this right.

More importantly, while the Tx-/Tx+ convention is universal, the A/B seems not to be, and it appears Waveshare and Schneider don't agree on which is A and which is B. So I got the wiring switched the wrong way. Some Schneider docs only show A/B which makes it even worse. Beware of A/B, only trust Tx-/Tx+. I did try to switch the wires but due to the other error it wouldn't work either.

My setup worked until I added devices to the bus. When I did that, I had to rewire the whole bus and this is probably when I switched Tx+/- the wrong way due to the A/B ambiguity.

I also learnt in the process that some gateways and devices support 4-wire Modbus. I tried a Teltonika gateway that has Rx+/Rx-/Tx+/Tx- pins and it wouldn't work until I connected Tx- and Rx-, and Tx+ and Rx+ together.

Source Link
Jérôme
Jérôme
  • 149
  • 6

I got help from someone more knowledgeable on the matter and got is sorted out. There were a few issues.

Here's a few pieces of information I would have been happy to find somewhere on the Internet when I was stuck.

In the waveshare configuration UI, there is a "Multi-Host Settings" section. I have no idea what multi-host means so I left if untouched. It appears I needed to set Protocol to "Modbus TCP to RTU". Might sound obvious, but due to the name of the section, I didn't even try anything there. I guess on my earlier working setup I touched everything and had this right.

More importantly, while the Tx-/Tx+ convention is universal, the A/B seems not to be, and it appears Waveshare and Schneider don't agree on which is A and which is B. So I got the wiring switched the wrong way. Some Schneider docs only show A/B which makes it even worse. Beware of A/B, only trust Tx-/Tx+. I did try to switch the wires but due to the other error it wouldn't work either.

My setup worked until I added devices to the bus. When I did that, I had to rewire the whole bus and this is probably when I switched Tx+/- the wrong due to the A/B ambiguity.

I also learnt in the process that some gateways and devices support 4-wire Modbus. I tried a Teltonika gateway that has Rx+/Rx-/Tx+/Tx- pins and it wouldn't work until I connected Tx- and Rx-, and Tx+ and Rx+ together.