Hi, I’ve seen this asked on some internetforums and I really needed it to debug Python code so this is how to do it if you just have RX, TX and GND at hand.
Connect CTS+RTS and CD+DTR+DSR on the PC side with wires to loop the hw handshake.
Edit the TelitSerialPortMux.exe with a Hex editor and replace the K1 in the modem initstring with K0.
Done. Start the TelitSerialPortMux and when the first new virtual serial port is opened by another terminal program on the PC, the modem will be contacted with an ATE1 command. If the PC receives an OK, the initialisation of the modem begins with ATE1&D2&K0&S0I4 followed by AT#CMUXMODE=1. When the last virtual comport is closed, it will disable the CMUX protocol on the modem.
The CMUX protocol uses it’s own handshaking. It also allows faster download with ScrDownloader as it can use a virtual port and HW handshake on that virtual wire 😉
Enjoy! /Anders H.
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