BGS2T RS485 not responding | Telit Cinterion IoT Developer Community
March 6, 2019 - 6:09pm, 2559 views
I have a microcontroller connected to the interface of a BGS2T-RS485 via an RS485 driver that I have successfully used to communicate with other devices, so I'm pretty sure that the hardware setup is correct, but no matter what bit-rate I use I never seen any response from the module. I can see the A and B lines responding to the microcontroller transmissions, but I never see any response from the module.
This module has never been used before, so should be in the default state.
I have tried bit-rates of: 1200, 2400, 4800, 9600, 19200, 38400, 57600, 115200 and 230400, none of which provide any repsonse.
Does anyone know what the default bit-rate is?
IGN is high, the module is powered from a 3S lithium ion battery pack (~12V) and delivers 5V from the 5V pin which supplies my microcontroller happily. It also seems to connect to the network as it flashes orange once every 3s.
Any hints gratefully received!
I have also observed that the state of the IGN input seems to make no difference to anything. I assumed that if it was pulled low it would turn the module off, but it seems to make no difference at all (even if grounded at power on): the LEDs flash just the same and it draws the same amount of current (a few tens of mA). Do I have a duff module?
The module's default baudrate is 115200 and module's RS785 can work with baudrates from 1200bps to 115200bps.
Have you connected the lines correctly in the right order? Have you connected the terminal's ground to your device's ground?
There's ***13487 inside the terminal. It has 120 Ohm line terminator and 680 Ohm pull-up and pull-down resistors.
If you suspect that the module or terminal might be out of order you could also open the terminal's casing and connect to ***13487 RX/TX lines (1 and 4) and check if the module is replying.
Thanks for the response: I removed the BGS2T from its case as you suggested and had a poke around with an oscilloscope probe. Sure enough there was no signal coming back from the module. In fact the transceiver chip was behaving very strangely: nice clean signal on A and B going in, but horrible mangled signal coming out of the receive line. To cut a long story short, after touching a soldering iron and a dab of solder to each of the legs on the ***13487 it now works. I think maybe there was a "dry" solder joint on either VCC or GND. Anyway I now have reliable communication going.
Thank you for this information. I've never expected that my advice with case opening will result in such an outcome. I rather thought that you will find the proof that there must be some problem in the circuit outside the BGS2T terminal...
Honestly I haven't heard about such a case before so I hope that it was only an incident, maybe the device has fallen down somewhere or something. I'm sure that there must be some basic communications tests done in the factory.
Anyway it's good that the problem is solved and it works now.
I'm always amazed when it's not my circuit that is the problem... but it does occasionally happen :-)
I'm about to buy two more from the same source, fingers-crossed!