1. Hardware
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under

2. Intel MCS-51 family of microcontrollers
On-chip Code Memory
On-chip Data Memory
Timers
8051
4K ROM
128 bytes 2
8031
8751
4K EPROM
8052
8K ROM
256 bytes 3
8032
8752
8K EPROM
In addition:
four 8-bit input/output (I/0) ports
serial interface
64K external code memory space
64K external data memory space
Boolean processor
210 bit-addressable locations
4us multiply/divide

3. Pinout

4. Pins
Port 0
I/O port.
Port 1
Port 2
Port 3
RST
Reset.
For resetting the 8051 (ie; loading the PC with the correct startup value).
EA-bar 
External access.
For enabling or disabling the on-chip ROM.
ALE
Address latch enable.
For latching the low byte of the address
PSEN-bar 
Program store enable.
For fetching instructions from external code memory.

5. Port 3 Pin Name Bit Address Function P3.0 RXD B0H
Receive data for serial port
P3.1
TXD
B1H
Transmit data for serial port
P3.2
INT0-bar
B2H
External interrupt 0
P3.3
INT1-bar
B3H
External interrupt 1
P3.4 T0
B4H
Timer/counter 0 external input
P3.5 T1
B5H
Timer/counter 1 external input
P3.6
WR-bar
B6H
External data memory write strobe
P3.7
RD-bar
B7H
External data memory read strobe