Difference between AT89C51 AT89C52 and AT89C2051

Parameter	AT89C51	AT89C52	AT89C2051
Flash Memory Size	4K Bytes of In-System Reprogrammable Flash Memory	8K Bytes of In-System Reprogrammable Flash Memory	2K Bytes of Reprogrammable Flash Memory
Endurance	1,000 Write/Erase Cycles	1,000 Write/Erase Cycles	10,000 Write/Erase Cycles
Data Memory Size	128 X 8 bit internal RAM	256 X 8 bit internal RAM	128 x 8-bit Internal RAM
Operating Voltage	5V (up to 6.6V)	5V (up to 6.6V)	2.7V to 6V
Programmable I/O Lines	32	32	15
Timers/Counters	Two 16 bit	Three 16 Bit	Two 16 bit
Interrupt Sources	Six	Eight	Six
Power Saving Modes	Low Power Idle and Power Down	Low Power Idle and Power Down	Low-power Idle and Power-down Modes
Pins	PQFP/TQFP=44 PDIP=40 PLCC=44	PQFP/TQFP=44 PDIP=40 PLCC=44	PDIP/SOIC=20
Program Memory Lock	Three Level Program Memory Lock	Three Level Program Memory Lock	Two-level Program Memory Lock
Channel	Programmable Serial Channel	Programmable Serial Channel	Programmable Serial UART Channel
Direct LED Output	Not Available	Not Available	Available
On-chip Analog Comparator	Not Available	Not Available	Available
Green (Pb/Halide-free) Packaging Option	Not Available	Not Available	Available