Current loop problem

[stoyanoff]

Greetings! I`m trying to make a current loop. Here is my schematicView attachment current loop.pdf
When I connected it through the another node(I`ll call it "slave" and my node should be "master"), I`m receiving my data correctly. As you can see the current loop is pumping pulses on both receivers. The 6n136 is fast enough and there is no delay, the baud rate is correct. I`m using UART with invert polarity set on TX and RX, because 6n136 inverts data! The problem is the slave doesn`t respond... When I use a market device it`s working, but my circuit doesn`t fit.. Any ideas?
PP: Baud rate and UART settings are correct!

 

[FvM]

As a first check, do you receive the transmitted data when the loop is closed?
Did you observe the current waveform with an oscilloscope?

 

[stoyanoff]

Yes! Everything seems fine! Time delay caused by the 6n136 is fine too. There are no time deviations. I`ve checked with logic analyzer on the back side(3.3V) - the baud rate and settings are correct!
I`ve tried to listen the market device and it`s all the same, but the node responds. Is there a chase something in my chart to prevent the slave from transmitting?
I`ll try to do a reverse engineering on the market device. I think they are using something similar to this Click for transmitting part. Or may be I have to put the transmitter into the positive part and loop to be closed to -15V.
I`m doing this for a very first time..
Thanks!