What interfaces are used to transfer data to the communication module (modem)?

Question

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What are the main interfaces used to transfer data to the communication module in mobile devices?
The module is controlled via the serial port with AT commands. And what basic interfaces are used for data transfer?

Answer 1

codepen.io/Geyan/pen/xEbxJp?editors=110

Answer 2

UART

Answer 3

There are also soft modems, where almost everything is emulated by drivers and designed as a pci / isa device.
I saw a very old isa hardware modem (some kind of acorp) where the device was physically connected via isa, but a com port appeared in the system.