The Global System for Mobile Communications (GSM) is a digital cellular system used for mobile devices. It is an international standard for mobile devices that is widely used for long distance communication. There are several GSM modules available in the market such as SIM900, SIM700, SIM800, SIM808, SIM5320, etc.
The SIM900A module allows users to send / receive data via GPRS, send / receive SMS and make / receive voice calls. It communicates in series with the devices as a microcontroller, PC using AT commands.
To interconnect the SIM900A module with the cellular network, it requires a SIM card provided by a network operator. For more information about Sim900A and how to use it, see the topic SIM900A GSM / GPRS Module in the sensors and modules section. The GSM / GPRS module uses the USART communication to communicate with the microcontroller or the PC terminal.
For information about USART in AVR ATmega16 / ATmega32 and how to use it, see the USART theme in AVR ATmega16 / ATmega32 in the inside section of ATmega.
![[Image: GSM%20Module.png]](http://www.electronicwings.com/public/images/user_images/images/ATmega_20160622/ATmega_GSM_SIM900A/GSM%20Module.png)
