Having a device RS-485 that can be set in two modes: ASCII and Modbus RTU.

With ASCII I get full functionality of the device, with Modbus only a few registers are available.

Which are the exact protocols working when a communication is established between a regular PC, and this device with a USB to RS485 converter?

RS - 485 is great to create a network of devices, Can a network be created in ASCII mode?

http://topsccc.com/htm/product/module/ex9036-m.htm

 

I am not real sure what you are asking. Modbus has two modes - one is called ASCII and the other RTU. They have exactly the same functionality.

It is possible that what you have is a system that supports an ASCII based protocol of their own making along with Modbus RTU. maybe in the RTU version they only allow access to fewer things. Who knows? Would be helpful if you mentioned just what it is so people could comment more intelligently.

ASCII just means it uses ASCII characters. they are handy because you can directly read the stream. Modbus RTU uses binary characters so the stream is not as easy to decipher to the human eye at a quick glance.

--
Bob
http://ilbob.blogspot.com/

 

Sure, you can have custom ASCII and binary protocols to multiple devices on the same 485 line (that's what Modbus is doing after all) and coincidentally, I've done that very thing.

The key is that there needs to be some kind of traffic control, such as node numbers. All the slaves are going to hear all the master commands, so they need some way to know a given command is not intended for them and not to respond until hearing one that is for them, and the protocol handling inside them needs to be written to do that.

If these devices satisfy that, then you're golden.

 

The manual says that the module defaults to Modbus RTU on power-up (pg 45).

The mode can be changed from Modbus to character based (pg 33).

The AA characters (in the character string) represent the module address in the character based comm mode. That would indicate that character based queries can query specific slave modules, a requirement for a 485 network.

 

Check the number of data bits you have configured.

Modbus ASCII might just work with 7 data bits where as Modbus RTU requires 8 data bits.