31-01-2013, 11:17 AM
8051 Microcontroller
[attachment=49027]
Overview
The Intel 8051 is a very popular general purpose microcontroller widely used for small scale embedded systems. Many vendors such as Atmel, Philips, and Texas Instruments produce MCS-51 family microcontroller chips.
The 8051 is an 8-bit microcontroller with 8 bit data bus and 16-bit address bus. The 16 bit address bus can address a 64K( 216) byte code memory space and a separate 64K byte of data memory space. The 8051 has 4K on-chip read only code memory and 128 bytes of internal Random Access Memory (RAM)
Besides internal RAM, the 8051 has various Special Function Registers (SFR) such as the Accumulator, the B register, and many other control registers.
34 8-bit general purpose registers in total.
The ALU performs one 8-bit operation at a time.
Two 16 bit /Counter timers
3 internal interrupts (one serial), 2 external interrupts.
4 8-bit I/O ports (3 of them are dual purposed). One of them used for serial port,
Some 8051 chips come with UART for serial communication and ADC for analog to digital conversion.
40 pins on the 8051 chip.
Most of these pins are used to connect to I/O devices or external data and code memory.
4 I/O port take 32 pins(4 x 8 bits) plus a pair of XTALS pins for crystal clock
A pair of Vcc and GND pins for power supply (the 8051 chip needs +5V 500mA to function properly)
A pair of timer pins for timing controls, a group of pins (EA, ALE, PSEN, WR, RD) for internal and external data and code memory access controls
One Reset pin for reboot purpose
The Pin Connection for External Code and Data Memory
The EA' (External Access) pin is used to control the internal or external memory access.
The signal 0 is for external memory access and signal 1 for internal memory access.
The PSEN' (Program Store Enable) is for reading external code memory when it is low (0) and EA is also 0.
The ALE (Address Latch Enable) activates the port 0 joined with port 2 to provide 16 bit external address bus to access the external memory. The ALE multiplexes the P0:
1 for latching address on P0 as A0-A7 in the 16 bit address buss, 0 for latching P0 as data I/O.
P0.x is named ADx because P0 is multiplexed for Address bus and Data bus at different clock time.
WR' only provides the signal to write external data memory
RD' provides the signal to read external data and code memory.
System Clock and Oscillator Circuits
The 8051 requires an external oscillator circuit. The oscillator circuit usually runs around 12MHz. the crystal generates 12M pulses in one second. The pulse is used to synchronize the system operation in a controlled pace..
A machine cycle is minimum amount time a simplest machine instruction must take
An 8051 machine cycle consists of 12 crystal pulses (clock cycle).
instruction with a memory oprand so that it needs multiple memory accesses.
[attachment=49027]
Overview
The Intel 8051 is a very popular general purpose microcontroller widely used for small scale embedded systems. Many vendors such as Atmel, Philips, and Texas Instruments produce MCS-51 family microcontroller chips.
The 8051 is an 8-bit microcontroller with 8 bit data bus and 16-bit address bus. The 16 bit address bus can address a 64K( 216) byte code memory space and a separate 64K byte of data memory space. The 8051 has 4K on-chip read only code memory and 128 bytes of internal Random Access Memory (RAM)
Besides internal RAM, the 8051 has various Special Function Registers (SFR) such as the Accumulator, the B register, and many other control registers.
34 8-bit general purpose registers in total.
The ALU performs one 8-bit operation at a time.
Two 16 bit /Counter timers
3 internal interrupts (one serial), 2 external interrupts.
4 8-bit I/O ports (3 of them are dual purposed). One of them used for serial port,
Some 8051 chips come with UART for serial communication and ADC for analog to digital conversion.
40 pins on the 8051 chip.
Most of these pins are used to connect to I/O devices or external data and code memory.
4 I/O port take 32 pins(4 x 8 bits) plus a pair of XTALS pins for crystal clock
A pair of Vcc and GND pins for power supply (the 8051 chip needs +5V 500mA to function properly)
A pair of timer pins for timing controls, a group of pins (EA, ALE, PSEN, WR, RD) for internal and external data and code memory access controls
One Reset pin for reboot purpose
The Pin Connection for External Code and Data Memory
The EA' (External Access) pin is used to control the internal or external memory access.
The signal 0 is for external memory access and signal 1 for internal memory access.
The PSEN' (Program Store Enable) is for reading external code memory when it is low (0) and EA is also 0.
The ALE (Address Latch Enable) activates the port 0 joined with port 2 to provide 16 bit external address bus to access the external memory. The ALE multiplexes the P0:
1 for latching address on P0 as A0-A7 in the 16 bit address buss, 0 for latching P0 as data I/O.
P0.x is named ADx because P0 is multiplexed for Address bus and Data bus at different clock time.
WR' only provides the signal to write external data memory
RD' provides the signal to read external data and code memory.
System Clock and Oscillator Circuits
The 8051 requires an external oscillator circuit. The oscillator circuit usually runs around 12MHz. the crystal generates 12M pulses in one second. The pulse is used to synchronize the system operation in a controlled pace..
A machine cycle is minimum amount time a simplest machine instruction must take
An 8051 machine cycle consists of 12 crystal pulses (clock cycle).
instruction with a memory oprand so that it needs multiple memory accesses.