Reading strings from modbus slaves result with wrong text

[Hoops123]

Hello,

 

I now have a few unitronics PLC's on site, I am getting more familiar with them but still fairly new.

I have an application where the PLC talks to a cobot over modbus, everthing works great, never had any problems with it. This morning i was asked if I could display the "current program" running on the cobot on the unitronics HMI. 

I thought it would be as easy as just reading a string data type.. 

I'm now thinking that to read the string, I read each interger in addresses 7701-7799 assuming that the numbers are Ascii code(manual doesnt say) then concatenate them to get the string.

Does anyone have experience of reading strings from modbus slaves??

[Gabriel Franco]

1. Create a new tag  buffer type (array long enough to hold string lenght) and a new tag string-ascii type.

2. Create a new Modbus operation using buffer name.

3. In ladder, use copy buffer to tag.

 

[Hoops123]

Brilliant!! worked a treat. Many thanks

[Hoops123]

I spoke to soon on this one. I thought it was working but I just didnt look at the result properly.

Each pair of letters in the string are switched.

So the cobot has a program in it called "320rpm" reading this over modbus (as above) and displaying the result on the HMI I get "23r0mp"

Anyone have any ideas on how to fix this one?

 

[Ausman]

As a Vision only user, that looks like an Endian problem, which would require some simple rearranging of data, in a consistent pattern for everything received. 

In Vision this is done with Swap Bytes, don't know what it is called in Unilogic, but have to assume it exists.

cheers, Aus

[Hoops123]

Thanks Aus,  it was an endian problem, unistream does have a swap bytes FB which done the job.