The SIM900A modem is a compact dual-band GSM module from SIMCom, operating on the 900/1800MHz frequencies. It can automatically detect available bands or be manually configured via AT commands. The baud rate is adjustable from 1200 to 115200 bps, providing flexible communication options.

Designed for both PC and microcontroller interfacing, the modem features RS232 support through an onboard MAX232 chip. It supports voice calls, SMS, and GPRS data transmission, making it ideal for M2M and IoT applications. With an onboard regulated power supply, it accepts a wide range of input voltages for easy integration.

The SIM900A also offers TTL and serial outputs, enabling seamless connectivity and control through simple AT commands. Its ultra-compact SMT form factor makes it perfect for space-constrained, embedded designs.