No response from the EGX81 modem

[Anonimo]

The requirement is to test the EGX81 device as an upgrade for our existing BGS2T devices. We currently use this device at nine remote sites where a 2G to 4G upgrade is required. The following details the EGX81 device setup and testing.

1. Testing carried out with Windows Laptop, Waveshare USB/RS232 Converter, Comms/DC Power Cables and 15V DC PSU, as used with existing BGS2T device. This test configuration has always worked with the BGS2T device (also earlier Siemens TC35) and we have never experienced any RS232 communication issues with these devices.
2. On power up the EGX81 green Led turns on and the orange Led flashes and then turns steady orange (with the antenna connected).
3. Using the BGS2T RS232 data cable (only TXD, RXD and ground wired), it is not possible to get a reply from the device using the AT+IPR=? command. We used this command using Terminal speeds between 300 baud and 115,200 baud but no acknowledgement message was received from the EGX81 for any. Other IPR commands were tried and again no reply from any.
4. In addition several different Terminal devices were used and no replies were received from the EGX81.
5. The device Leds appear to indicate that the EGX81 LTE interface is OK but the lack of any replies using the IPR commands, indicates a possible RS232 interface problem.
6. Is it possible that the EGX81 device requires some change to the RS232 wiring?
7. We have searched your forums but unfortunately no help found.
8. Any suggestions would be welcome

[Sergio Bertana]

If you read this topic, you will probably find the solution to your problem.

Unlike previous models, the Telit EGX81-W modem does not support auto-baud rate detection. By default, the communication settings are 115200, N, 8, 1. The modem also does not transmit data when the CTS signal is low. Therefore, you must use a modem cable that correctly handles hardware flow control. The RTS output on the DTE side (pin 7) must be connected to the CTS input on the DCE side (pin 7).

Here is a screenshot of our free Toolly program with the correct settings, along with the response to the AT+IPR=? command.

[Anonimo]

The modem cable wiring I currently use is 3 wire only (TXD, RXD and GND) with no CPU operation of the control lines. This configuration works ok for the BGS2T modem.

The topic you refer to suggests I need to connect the modem DTR and RTS to +V to achieve a reply form the modem.  Can you please confirm?

Because this is an upgrade to existing equipment using the BGS2T modem, software modifications would not be easy.

[Sergio Bertana]

To activate the modem’s RTS signal (pin 7 on the female DB9 connector), you must connect it to +V.

Since the modem’s RTS signal (pin 8 on the female DB9 connector) is at +V by default, you can simply short pins 7 and 8 together to allow the modem to transmit data.

Anyway, you can disable the modem’s flow control. If you check the EXS82-W AT Command Set (available on our website), you’ll find the AT\Q command, which allows you to configure flow control on the EXS82-W.

In your case, if you want the modem to be able to transmit data regardless of the CTS signal state, you can send the AT\Q0 command to disable flow control. After that, you can send the AT&W command to save the configuration. The modem will then be able to operate using only three wires.

Please remember to use the AT+IPR command to set the desired baud rate. Then, use the AT&W to save the configuration.

[Autore]

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