Basic Microcontroller

What is Microcontroller?

A microcontroller is a small computer on a single integrated circut containing a processor core, memory, and programmable input/output peripherals. Microcontrollers are designed for embedded applications, in contrast to the microprocessors used in personal computers or other general purpose applications consisting of various discrete chips. Microcontrollers are used in automatically controlled products and devices, such as automobile engine control systems, implantable medical devices, remote controls, office machines, appliances, power tools, toys and other embedded systems. By reducing the size and cost compared to a design that uses a separate microprocessor, memory, and input/output devices, microcontrollers make it economical to digitally control even more devices and processes.

Architecture of 8051 Microcontroller 

Pin Diagram of 8051 Microcontroller

Pin Description of 8051 Microcontroller

Pin No	Function	Name
1	8 bit input/output port (P1) pins	P1.0
2	8 bit input/output port (P1) pins	P1.1
3	8 bit input/output port (P1) pins	P1.2
4	8 bit input/output port (P1) pins	P1.3
5	8 bit input/output port (P1) pins	P1.4
6	8 bit input/output port (P1) pins	P1.5
7	8 bit input/output port (P1) pins	P1.6
8	8 bit input/output port (P1) pins	P1.7
9	Reset pin; Active high	RST
10	Input (receiver) for serial communication	RxD
	8 bit input/output port (P3) pins	P3.0
11	Output (transmitter) for serial communication	TxD
	8 bit input/output port (P3) pins	P3.1
12	External interrupt 1	INT0
	8 bit input/output port (P3) pins	P3.2
13	External interrupt 2	INT1
	8 bit input/output port (P3) pins	P3.3
14	Timer1 external input	T0
	8 bit input/output port (P3) pins	P3.4
15	Timer2 external input	T1
	8 bit input/output port (P3) pins	P3.5
16	Write to external data memory	Write (WR)
	8 bit input/output port (P3) pins	P3.6
17	Read from external data memory	Read (RD)
	8 bit input/output port (P3) pins	P3.7
18	Quartz crystal oscillator (up to 24 MHz)	XTAL1
19	Quartz crystal oscillator (up to 24 MHz)	XTAL2
20	Ground; 0V	Ground
21	8 bit input/output port (P2) pins	P2.0
	High-order address bits when interfacing with external memory	A8
22	8 bit input/output port (P2) pins	P2.1
	High-order address bits when interfacing with external memory	A9
23	8 bit input/output port (P2) pins	P2.2
	High-order address bits when interfacing with external memory	A10
24	8 bit input/output port (P2) pins	P2.3
	High-order address bits when interfacing with external memory	A11
25	8 bit input/output port (P2) pins	P2.4
	High-order address bits when interfacing with external memory	A12
26	8 bit input/output port (P2) pins	P2.5
	High-order address bits when interfacing with external memory	A13
27	8 bit input/output port (P2) pins	P2.6
	High-order address bits when interfacing with external memory	A14
28	8 bit input/output port (P2) pins	P2.7
	High-order address bits when interfacing with external memory	A15
29	Program store enable; Read from external program memory	PSEN
30	Address Latch Enable	ALE
	Program pulse input during Flash programming	PROG
31	External Access Enable;  Vcc for internal program executions	EA
	Programming enable voltage; 12V (during Flash programming)	Vpp
32	8 bit input/output port (P0) pin	P0.7
	Low-order address bits when interfacing with external memory	AD7
33	8 bit input/output port (P0) pins	P0.6
	Low-order address bits when interfacing with external memory	AD6
34	8 bit input/output port (P0) pin	P0.5
	Low-order address bits when interfacing with external memory	AD5
35	8 bit input/output port (P0) pin	P0.4
	Low-order address bits when interfacing with external memory	AD4
36	8 bit input/output port (P0) pin	P0.3
	Low-order address bits when interfacing with external memory	AD3
37	8 bit input/output port (P0) pin	P0.2
	Low-order address bits when interfacing with external memory	AD2
38	8 bit input/output port (P0) pin	P0.1
	Low-order address bits when interfacing with external memory	AD1
39	8 bit input/output port (P0) pin	P0.0
	Low-order address bits when interfacing with external memory	AD0
40	Supply voltage; 5V (up to 6.6V)	Vcc