AT89C51 is an 8-bit microcontroller and belongs to Atmel’s 8051 family. ATMEL 89C51, has 4KB of Flash programmable and erasable read only memory (PEROM) and 128 bytes of RAM. It can be erased and program to a maximum of 1000 times.
In 40 pin AT89C51, there are four ports designated as P1, P2, P3 and P0. All these ports are 8-bit bi-directional ports i.e., they can be used as both input and output ports. Except P0 which needs external pull-ups, rest of the ports have internal pull-ups. When 1s are written to these port pins, they are pulled high by the internal pull-ups and can be used as inputs. These ports are also bit addressable and so their bits can also be accessed individually.
Port P0 and P2 are also used to provide low byte and high byte addresses, respectively, when connected to an external memory. Port 3 has multiplexed pins for special functions like serial communication, hardware interrupts, timer inputs and read/write operation from external memory. AT89C51 has an inbuilt UART for serial communication. It can be programmed to operate at different baud rates. Including two timers hard interrupts, it has a total of six interrupts.
Features and Specifications of 89C51:
• 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
Datasheet:
AT89C51 Microcontroller
Pin Description
Pin Number
Pin Name
Description
1
P1.0
0th pin of PORT P1
2
P1.1
1st pin of PORT P1
3
P1.2
2nd pin of PORT P1
4
P1.3
3rd pin of PORT P1
5
P1.4
4th pin of PORT P1
6
P1.5
5th pin of PORT P1
7
P1.6
6th pin of PORT P1
8
P1.7
7th pin of PORT P1
9
RST
Reset pin of the Microcontroller
10
(RXD) P3.0
0th pin of PORT P3 or Receiver pin of Microcontroller
11
(TXD) P3.1
1st pin of PORT P3 or Transmitter pin of Microcontroller
12
(INT0) P3.2
2nd pin of PORT P3 or External Interrupt 0 of MCU
13
(INT1) P3.3
3rd pin of PORT P3 or External Interrupt 1 of MCU
14
(T0) P3.4
4th pin of PORT P3 or Timer 0 interrupt of MCU
15
(T1) P3.5
5th pin of PORT P3 or Timer 1 interrupt of MCU
16
(WR) P3.6
6th pin of PORT P3 or Write to External data memory pin
17
(RD) P3.7
7th pin of PORT P3 or Read from External data memory pin
18
XTAL2
External crystal pin 2 of Microcontroller
19
XTAL1
External crystal pin 1 of Microcontroller
20
GND
Ground pin of MCU
21
P2.0(A8)
0th pin of PORT P2 or High-order Address bit 8 of MCU
22
P2.1(A9)
1st pin of PORT P2 or High-order Address bit 9 of MCU
23
P2.2(A10)
2nd pin of PORT P2 or High-order Address bit 10 of MCU
24
P2.3(A11)
3rd pin of PORT P2 or High-order Address bit 11 of MCU
25
P2.4(A12)
4th pin of PORT P2 or High-order Address bit 12 of MCU
26
P2.5(A13)
5th pin of PORT P2 or High-order Address bit 13 of MCU
27
P2.6(A14)
6th pin of PORT P2 or High-order Address bit 14 of MCU
28
P2.7(A15)
7th pin of PORT P2 or High-order Address bit 15 of MCU
29
PSEN
Program store enable pin, Read external program memory
30
ALE/PROG
Address Latch Enable/ Program Pulse input for flashing
31
EA/VPP
Access Enable voltage/Program enable voltage
32
P0.7(AD7)
7th pin of PORT P0 or Low-order Address bit 7 of MCU
33
P0.6(AD6)
6th pin of PORT P0 or Low -order Address bit 6 of MCU
34
P0.5(AD5)
6th pin of PORT P0 or Low -order Address bit 5 of MCU
35
P0.4(AD4)
6th pin of PORT P0 or Low -order Address bit 4 of MCU
36
P0.3(AD3)
3rd pin of PORT P0 or Low -order Address bit 3 of MCU
37
P0.2(AD2)
2nd pin of PORT P0 or Low -order Address bit 2 of MCU
38
P0.1(AD1)
1st pin of PORT P0 or Low -order Address bit 1 of MCU
39
P0.0(AD0)
0th pin of PORT P0 or Low -order Address bit 0 of MCU
40
Vcc
Supply pin of MCU
Datasheet:
The AT89C51 datasheet of the Microcontroller
Other ATMEL MCU’s
AT89S52, ATMega328P,
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