ATMEL 89C51 MICROCONTROLLERS

The Atmel AT89 series is an Intel-8051-compatible family of 8 bit microcontrollers (µCs) manufactured by the Atmel Corporation.
Based on the Intel 8051 core, the AT89 series remains very popular as general purpose microcontrollers, due to their industry standard instruction set, and low unit cost
This allows a great amount of legacy code to be reused without modification in new applications.
While considerably less powerful than the newer AT90 series of AVR RISC microcontrollers, new product development has continued with the AT89 series for the aforementioned advantages.
Of more recent times, the AT89 series has been augmented with 8051-cored special function microcontrollers, specifically in the areas of USB, I²C(TWI), SPI and CAN bus controllers, MP3 decoders and hardware PWM
AT89 Series Microcontrollers


Device name Data Memory

AT89C1051 1K Flash 64 RAM

AT89C2051 2K Flash 128 RAM

AT89C51 4K Flash 128 RAM

AT89C52 8K Flash 256 RAM

AT89C55 20K Flash 256 RAM

AT89S82 528K Flash 256 RAM

AT89S53 12K Flash 256 RAM


Description
The AT89C51 is a low-power, high-performance CMOS 8-bit microcomputer with 4Kbytes of Flash programmable and erasable read only memory (PEROM).

The device is manufactured using Atmel’s high-density nonvolatile memory technology and is compatible with the industry-standard MCS-51 instruction set and pin out
.
The on-chip Flash allows the program memory to be reprogrammed in-system or by a conventional nonvolatile memory programmer.

By combining a versatile 8-bit CPU with Flash on a monolithic chip, the Atmel AT89C51 is a powerful microcomputer which provides a highly-flexible and cost-effective applications solution to many embedded control

89C51
All four ports in the AT 89C51 are bidirectional.
Each consists of a latch (Special Function Registers P0 through P3), an output driver, and an input buffer.
The output drivers of Ports 0 and 2, and the input buffers of Port 0, are used in accesses to external memory.
In this application, Port 0 outputs the low byte of the external memory address, time-multiplexed with the byte being written or read.
Port 2 outputs the high byte of the external memory address when the address is 16 bits wide.
Otherwise the Port 2 pins continue to emit the P2 SFR content.
All the Port 3 pins, and two Port 1 pins (in the AT89C52)are multifunctional.
The alternate functions can only be activated if the corresponding bit latch in the port SFR contains a 1. Otherwise the port pin is stuck at 0.
]
FEATURES
• Compatible with MCS-51™ Products

• 4K Bytes of In-System Reprogrammable Flash Memory

– Endurance: 1,000 Write/Erase Cycles

• Fully Static Operation: 0 Hz to 24 MHz

• Three-level Program Memory Lock

• 128 x 8-bit Internal RAM

• 32 Programmable I/O Lines

• Two 16-bit Timer/Counters

• Six Interrupt Sources

• Programmable Serial Channel

• Low-power Idle and Power-down Modes

PORT DESCRIPTION
There are totally four ports in micro controller as
• PORT 0
• PORT 1
• PORT 2
• PORT3

Port 0

• Port 0 is an 8-bit open-drain bi-directional I/O port.

• As an output port, each pin can sink eight TTL inputs.

• When 1sare written to port 0 pins, the pins can be used as high impedance inputs.

• Port 0 may also be configured to be the multiplexed low order
address/ bus during accesses to external program
and data memory.

• In this mode P0 has internal pullups.

• Port 0 also receives the code bytes during Flash programming,
and outputs the code bytes during program verification.

• External pull ups are required during program verification.


Port 1
• Port 1 is an 8-bit bi-directional I/O port with internal pullups.

• The Port 1 output buffers can sink/source four TTL inputs.

• When 1s are written to Port 1 pins they are pulled high by
the internal pullups and can be used as inputs.

• As inputs,Port 1 pins that are externally being pulled low will sourcecurrent (IIL) because of the internal pullups.

• Port 1 also receives the low-order address bytes during
Flash programming and verification.




Port 2
• Port 2 is an 8-bit bi-directional I/O port with internal pullups.

• The Port 2 output buffers can sink/source four TTL inputs.

• When 1s are written to Port 2 pins they are pulled high by
the internal pull ups and can be used as inputs.
• As inputs, Port 2 pins that are externally being pulled low will source current (IIL) because of the internal pullups.
• Port 2 emits the high-order address byte during fetches
From external program memory and during accesses toexternal data memory that use 16-bit addresses (MOVX @DPTR).

• In this application, it uses strong internal pullups
when emitting 1s.

• During accesses to external data memory
that use 8-bit addresses (MOVX @ RI), Port 2 emits the
contents of the P2 Special Function Register.
• Port 2 also receives the high-order address bits and some
control signals during Flash programming and verification.


Port 3

• Port 3 is an 8-bit bi-directional I/O port with internal pullups.

• The Port 3 output buffers can sink/source four TTL inputs.

• When 1s are written to Port 3 pins they are pulled high by
the internal pullups and can be used as inputs.
• As inputs,Port 3 pins that are externally being pulled low will sourcecurrent (IIL) because of the pullups.

Port 3 also serves the functions of various special features
of the AT89C51 as listed below:

Port Pin Alternate Functions

P3.0 RXD serial input port

P3.1 TXD serial output port

P3.2 INT0 external interrupt 0

P3.3 INT1 external interrupt 1

P3.4 T0 timer 0 external input

P3.5 T1 timer 1 external input

P3.6 WR external data memory write strobe

P3.7 RD external data memory read strobe