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I need to connect the TRB255 to an ARM computer with a 2-wires RS485 connection. I short-circuited R+/D+ and R-/D- as per your manual.

Now I'm trying to send AT commands from the ARM computer but I get no answer from the modem. I'm simply doing an

echo AT > /dev/ttyS1

and, on another terminal,

cat /dev/ttyS1

Current configuration is 9600, databits 8, parity None stopbits 1, flow control None, serial type Console, Full Duplex OFF

1 Answer

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Hello,

First of all, I would suggest double-checking your wire (is it working with other devices, and if you 100% correctly connected wires as this guide shows: https://wiki.teltonika-networks.com/view/TRB255_RS485#2-Wire_and_4-Wire_Networks)

Secondly, you could play around with configuration settings, changing baud rate, data bits. Also, I would like to know what is connected to the other end of the RS485 cable.

Regards.
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Yes, I followed exactly that guide to connect the wires. On the other side there is an electronic board running Linux, on an ARM processor with a RS485 port. Should I power off/on the modem when I change the settings? Also, is the procedure I'm following correct from a global point of view?
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Ok, I success in communicating in RS485. Now I expected to send AT commands with the modem responding, but instead I receive "password". I think the modem is asking me to authenticate in a kind of console, but I just want to send commands and get responses to them
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Hello,

First of all, you must authenticate by using the default username root and your WebUI password.
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sorry, I think the point is not clear. I need to send SMS programmatically (in C language) using this modem connected to an RS485 port.

With the modems I used so far, I simply opened the serial port and send AT commands with a write to the port.
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Unfortunately, this is not the case with our routers. You need to authenticate atleast once before sending any commands.