8051 Microcontroller

• High Performance HMOS processor
• Boolean Processor
• Internal Timers/Event Counters
• Bit-Addressable RAM
• 2-level Interrupt Priority Structure
• Programmable Full duplex Serial Channel
• 32 I/O lines (Four 8-bit ports)
• 64K Program Memory Space
• 111 instructions (64 Single Cycle)
• Security Feature Protects EPROM Parts Against Software Piracy
• 64K Data Memory Space

Architecture of 8051

PIN Diagram

Pin Description:

Vcc: Supply Voltage

Vss: Circuit Ground

Port 0:Port 0 is an 8-bit open drain bidirectional I/O port. As an output port each pin can sink 8 LS TTL inputs.

Port 0 pins that have 1s written to them float, and in that state can be used as high-impedance inputs

Port 0 is also the multiplexed low order address and data bus during accesses to external Program and data memory. In this application it uses strong internal pullups  when emitting 1s and can source and sink 8 LS TTl inputs.

Port 0 is also receives the code bytes during programming of the EPROM parts, and outputs the code bytes during program verification of the  ROM and EPROM parts. External pullups are required during program verification.

Port 1: Port 1 is an 8-bit bidirectional I/O port with internal pullups. the Port 1 output buffer can sink/source 4 LS TTL inputs. Port 1 pins that have 1s written  to them are pulled high by the internal pullups, and in that state can be used as inputs. As inputs, Port 1 pins that are externally  being pulled low  source current  because of the internal pullups.

Port 1  also receives the lower order  address bytes  during programming of the EPROM parts and during program verification of the  ROM and EPROM parts.

Port 2: Port 2 is an 8-bit bidirectional I/O port with internal pullups. the Port 2 output buffers can sink / source 4 LS TTL inputs. Port 2 pins that have  1s written to them  are pulled high  by the internal pullups, and in that state can be used as inputs. As inputs, Port 2 pins  that are externally being pulled low  will source current because of the internal pullups.

Port 2 emits the high-order  address byte during fetches from external program memory and during access  to external data memory that use 16-bit addresses. In this application it uses strong  internal pullups when emitting 1s. During accesses to external data memory  that use 8-bit addresses, Port 2 emits the content of the P2  special function register.

Port 2 also receives the high-order address bits during  programming of the EPROM parts and during  program verification of the ROM and EPROM parts.

Port 3:  Port 3 is an 8-bit bidirectional I/O port with internal pullups. The Port 3 output buffers can sink/source 4 LS TTL inputs.Port 3 pins that have 1s written  to them are pulled  high by the internal pullups, and in that state can be used  as inputs. As inputs, Port 3 pins  that are externally being pulled  low will source current because of the internal pullups.

Port 3  also serves  the functions of various special features 

Port Pin	Alternative Function
P3.0	RXD (serial input port>
P3.1	TXD (serial output port)
P3.2	External interrupt 0
P3.3	External interrupt 1
P3.4	T0 ( Timer 0 External input)
P3.5	T1 ( Timer 1 External input)
P3.6	External data memory Write strobe
P3.7	External data memory Read strobe

RST: Reset Input. A high on this pin for two machine cycles while the Oscillator is running resets the device.