Switching from Data Mode to Command Mode


#1

Hi,

The Hologram Nova is built on the Ubox SARA R410M-02B module. I’m using this device with an Orange Pi (similar to Raspberry Pi) running Armbian Ubuntu. The problem I’m trying to solve is:

once a ppp connection is established, I am not able to send AT commands to the device and get responses.

I am not using the Hologram API or CLI. Rather, I am using wvdial to establish a ppp connection.

I know how to load the correct drivers and then I see four USB devices appear:

/dev/ttyUSB1
/dev/ttyUSB2
/dev/ttyUSB3
/dev/ttyUSB4

Before I establish the ppp connection, I can open /dev/ttyUSB2, send AT commands and read responses. I am not able to interact with the device using any of the other /dev/ttyUSBx devices.

In this document:

on page 11, section 1.1, the document describes:
command mode: device accepts and responds to AT commands
data mode: the device has connected and sends data back and forth
Online command mode: “the DCE has a data connection established with a remote party, but treats signals
from the DTE as command lines and sends back responses and unsolicited”

In the next section, “1.1.1 Switch from data mode to online command mode,” it says:

“It is possible to switch from data mode to online command mode (when a data connection is established) in
the following ways:
• with the escape sequence: for more details see the S2 command description
• via a DTR transition: during data mode, the current DTR state is not important, but only its transition.
Furthermore, only the DTR transition from ON to OFF is detected; it can be used to control the switch to
online command mode, or to command mode (the data connection is released). For more details see the
Table 6 and the Table 7”

I don’t believe it is possible to switch the Nova via a DTR transition because I do not believe it is possible to control the DTR line–but maybe I am wrong.

So, does anyone know how to send the escape sequence referred to? I’m a bit confused because once the ppp session is established, I am sending UDP and TCP packets. I’m not clear on how to send the necessary escape sequence (default is “+++”). If I try to send a packet containing “+++” there will also be a bunch of header information.

Has anyone solved this problem?

Thanks and regards,

Matt


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