I tried to communicate with EG21-G module using CMUX mode, so later I can enable PPP protocol for internet connection. I send AT+CMUX=0 and the modem responded with OK. I wait for 5 seconds, and send two SABM Frame: 0xF90B2F01F1F9 and 0xF9032F01FDF9, but none of those frames is being responded. I see this thread that might have similar issue: MUX mode in EC21. So I pull the RTS pin to low, but the modem module still not responding. My EG21-G have latest version: EG21GGBR07A11M1G_A0.300.A0.300. Can you tell me what I’ve been missing to enable this CMUX mode so I can send and receive SABM frame to/from EG21-G module? Thank you for your assistance.
Hi,@krisna
Please use a complete serial cable (such as RS232) to connect to the main serial port, and then try to communicate through this serial port.
I do use RS232 cable that come from UMTS<E-EVB-KIT package (UMTS & LTE EVB kit | Quectel), and it’s connected to COM1 (MAIN). And I tried to set CMUX mode on Quectel USB AT Port, but it returns +CME ERROR: 3. So both RS232 and USB still cannot communicate using CMUX mode. Any advice? Thanks.
Thank you for sharing the CMUX documentation. Based on that document, I write this AT command:
AT+CMUX=0,0,5,127,10,3,30,10,2
The details:
0 = Basic options
0 = UIH frames used only
5 = Baudrate 115200
127 = Maximum frame size (default)
10 = Acknowledgement timer (default)
3 = Maximum number of re-transmissions (default)
30 = Response timer in ten milliseconds (default)
10 = Wake up response timer (default)
2 = Window size (unsupported)
It still doesn’t response to any SABM frame. And also from the last section of the document, I think EG21-G module should still give some response to AT+CMUX? command, but in reality, it just won’t response at all. I think the port is stuck/hang up. What do you think? Thanks.
Hi,@krisna
Can you get a response when you send other messages through this serial port? Is it only the SABM frame that gets no response or do all messages have no response?
I can get all AT responses before I set CMUX mode. After I set CMUX mode (either using AT+CMUX=0 or AT+CMUX=0,0,5,127,10,3,30,10,2), that’s when the cellular module doesn’t reply to any SABM frame or any AT command message. Thank you for your assistance.
I’m using Hercules (Hercules SETUP utility | HW-group.com) as serial port terminal. Here is the detail configuration on Hercules:
Name: COM14
Baud: 115200
Data size: 8
Parity: none
Handshake: RTS/CTS and OFF (tested both, results are the same)
Mode: Free
I’m using RS232 that come from Quectel EVB, connected to COM1 (MAIN) on EVB. Here is the logs, bracket <...> means my action, not real logs. Thank you for your support.
<switch to Text Mode>
<send> AT+QGMR
AT+QGMR
EG21GGBR07A11M1G_A0.300.A0.300
OK
<send> AT+CMUX?
AT+CMUX?
+CMUX: 0,0,0,0,0,0,0,0,0
OK
<send> AT+CMUX=0,0,5,127,10,3,30,10,2
AT+CMUX=0,0,5,127,10,3,30,10,2
OK
<send> AT+CMUX?
<send> AT+CMUX?
<send> AT+CMUX?
<send> AT+CMUX?
<send> AT+CMUX?
<send> AT+CMUX?
<switch to Hexadecimal Mode>
<send> {F9}{0B}{2F}{01}{F1}{F9} <send> {F9}{03}{2F}{01}{FD}{F9} <send> {F9}{0B}{2F}{01}{F1}{F9} <send> {F9}{03}{2F}{01}{FD}{F9}
Hi,@krisna
Sorry for the late reply.
1.Use AT+CMUX=0 on the uart port to enable CMUX. At this time, the uart has entered the cmux mode and cannot receive traditional AT commands.
2.use hex command in uart port to open channel,because uart port in CMUX mode, cannot receive traditional AT commands
Thank you for your detailed explanations. 0xF9033F011CF9 does works on EG21-G module, this is the SABM frame that I was looking for. I think both 0xF90B2F01F1F9 and 0xF9032F01FDF9 is working for other module, I found it somewhere on internet, but apparently it doesn’t work on EG21-G. And the reason why my MCU cannot talk using CMUX mode is because hardware control flow CTS need to be mate with RTS instead CTS, and vice versa. Now the CMUX works perfectly fine on my MCU after I rework the pin. Thank you for your support.
