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+--- Thread: Modbus Schneider PLCs (/showthread.php?tid=1274)
Modbus Schneider PLCs - iJAF - 05.03.2018
Hello Im trying to optimize a modbus communication on order to read from a tcp slave (it will be a schneider PLC) with a single request.
First I'm triyng with floats, this is my test which is sending 3 separated requests:
{"name":"Teste1","bus_datatype":"float32","type":"register","address":0,"writable":"true" },
{"name":"Teste2","bus_datatype":"float32","type":"register","address":2,"writable":"true" },
{"name":"Teste3","bus_datatype":"float32","type":"register","address":4,"writable":"true" }
I have tryed to implement the following json, but without success :
{"name":"Teste1","bus_datatype":"float32","type":"register","address":0,"writable":"true","Read_count":3,"Read_offset":0 },
{"name":"Teste2","bus_datatype":"float32","type":"register","address":0,"writable":"true","Read_count":3,"Read_offset":2 },
{"name":"Teste3","bus_datatype":"float32","type":"register","address":0,"writable":"true","Read_count":3,"Read_offset":4 }
Any sugestions ?
Thank you
RE: Modbus Schneider PLCs - admin - 05.03.2018
All JSON keys must be lowercase, but you have Read_count and Read_offset. read_count must be 6, it is counted in 16-bit registers so 2 x 3 in your case. Also, you are probably missing "datatype": "float32" for each profile entry.
RE: Modbus Schneider PLCs - iJAF - 05.03.2018
Thank you ! I will try it
But i have found another issue with float32.
I have to swap the 2x16bit registers themselves that create the correct float.
Reg0 = 3F80
Reg1 = 0000
to
Reg0 = 0000
Reg1 = 3F80
I have tried the read_swap="w" but I see no difference
Note: I'm using the json profiles
Any easy way to do this ?
Thank you
RE: Modbus Schneider PLCs - admin - 05.03.2018
Set swap to n, word swap (w) is set by default
RE: Modbus Schneider PLCs - iJAF - 06.03.2018
Hello,
The reading is working perfect now, but unfortunately when I try to write to one of the variables I'm only writing to the first one.
For example if I write for the third variable the value 22.0, this value will be written to the first one, in the slave !
I am using this simple profile:
{"name":"Teste1","bus_datatype":"14","datatype":"float32","type":"register","address":0,"writable":"true","read_count":6,"read_offset":0,"read_swap":"n" },
{"name":"Teste2","bus_datatype":"14","datatype":"float32","type":"register","address":0,"writable":"true","read_count":6,"read_offset":2,"read_swap":"n" },
{"name":"Teste3","bus_datatype":"14","datatype":"float32","type":"register","address":0,"writable":"true","read_count":6,"read_offset":4,"read_swap":"n" }
Am I doing anything wrong ?
Thank you
RE: Modbus Schneider PLCs - admin - 06.03.2018
For write to work you need to set address field correctly, but this will break single block read. We might add another field (write_address) for cases like you have in future releases.
For now you have two options:
1. Do not use block read at all
2. Create another set of registers with "write_only": true, disable writable for original registers and use their values as status objects in visualization. This will introduce a delay between status object update due to polling interval.