The Atmel ATMEGA128 series are a 8-bit Microcontrollers that provides the following features like 128 Kbytes of In-system programmable flash with read-while-Write capabilities, 4 Kbytes EEPROM, 4 Kbytes SRAM, 53 general purpose I/O lines, 32 general purpose working registers, Real Time Counter (RTC), four flexible Timer/Counters with compare modes and PWM, 2 USARTs, a byte oriented Two-wire Serial Interface, an 8-channel, 10-bit ADC with optional differential input stage with programmable gain, programmable Watchdog Timer with Internal Oscillator, an SPI serial port, IEEE std. 1149.1 compliant JTAG test interface, also used for accessing the On-chip Debug system and programming and six software selectable power saving modes. It is available in 64 pin TQFP package.

It has a Power-on Reset and Programmable Brown-out Detection
It has internal calibrated RC oscillator
It has an external and internal interrupt sources
It has Six sleep modes like Idle, ADC Noise Reduction, Power-save, Power-down, Standby, and Extended standby
A Software Selectable Clock Frequency
It has Global pull-up disable