What is cmgs? What kind of protocol does it offer? What is the explanation?

AT-CMGS (SIM module AT instruction) sends SMS instruction.

Instruction: Code that tells a computer to perform a special operation. Such as data transmission instruction, arithmetic operation instruction, bit operation instruction, program flow control instruction, character string operation instruction and processor control instruction.

The communication protocol between GSM module and computer adopts AT instruction set.

There should be no so-called communication protocol between GSM module and MCU. If there must be, it is the international standard GSM0707 protocol. In fact, this is the standard AT instruction set.

If the AT instruction set is understood as a protocol, each chip manufacturer will have its own different instruction set, and there is no universal AT instruction set. Of course, most vendors have similar instruction sets.