ABOUT 8051

 COMPARISION BETWEEN CISC AND RISC:

RISC (Reduced Instruction Set Computer) and CISC (Complex Instruction Set Computer) stands for two different competing philosophies in designing modern computer architecture. The difference between RISC and CISC can lie on many levels, many plausible arguments are put forward by both sides, such as code density, transistor counts, memory bottlenecks, complier and decode complexity etc. 

CISC computers are based on a complex instructions are executed by microcode. Microcode allows developers to change hardware design and still maintain backward compatibility with instructions for earlier computers by changing only microcode, thus makes a complex instruction set possible and flexible. While CISC designs allow a lot of hardware flexibility, the supporting of microcode and slows the microprocessor performance because of the number of operations that must be performed to execute each of CISC instruction. A CISC instruction set typically includes many instructions with different sizes and execution cycles, which makes CISC instructions harder to pipeline.

 RISC VERSUS CISC:

A CISC processor has most of the following properties:

•   Richer instruction set,  some simple, some very complex
•   Instructions generally take more than 1 clock to execute
•   Instructions with variable size
•   Instructions interface memory in multiple mechanisms with complex addressing modes.
•   No pipelining is used.
•   Upward compatibility within the family
•   Microcode control
• Work well with simpler compiler

                 As time passed, one of the non-RISC architecture with large market is the Intel x 86 families; it has some specific characteristics associated with CISC:

• Segmented memory model
•   Few registers
•   Crappy floating point performance

 DIFFRENCE BETWEEN CONTROLLER AND PROCESSOR:

 MICROCONTROLLER:

Microcontrollers are used in a wide number of electronic systems such as:

•   Engine management systems in automobiles.
•   Keyboard of a PC.
•   Electronic measurement instruments (such as digital millimeters, frequency oscilloscopes)
•   Printers.
•   Mobile phones.
•   Televisions, radios, CD players, tape recording equipment.
•   Hearing aids.
•   Security alarm systems, fire alarm systems, and building services systems

Microprocessor:

 Microprocessor is the integration of a number of useful functions into a single IC

 Package. These functions are:

•   The ability to execute a stored set of instructions to carry out user defined tasks.
•   The ability to be able to access external memory chips to both read and write  From the memory.

MICROCONTROLLER	MICROPROCESSOR
In built  memory	External  memory
Internal I/O Circuit	External I/O Circuit
More bit handling Instructions	Few bit handling instructions.
That we can interface a microcontroller Directly means, "for example we can directly connect a Keyboard to microcontroller to any of its ports".	Microprocessor we can't interface directly...we require a circuit board since it requires RAM, IC.....etc
Designed to perform a small set of specific functions	Designed to perform a wider set of general-purpose functions.
RISC architecture	CISC architecture

Pin Diagram

 

 Difference between 8031, 8051, 8052:

Controller	On-chip data memory	On chip program Memory	No of 16bit Timers/counters	No of vectored interrupts
8031	128	None	2	5
8051	128	4k ROM	2	5
8052	256	8k ROM	3	6

 PIN DESCRIPTION:

                        

 VCC                           Supply voltage.

GND                          Ground.

 PORT 0:

Port 0 is an 8-bit open drain bidirectional I/O port. As an output port, each pin can sink eight TTL inputs. When 1s are written to port 0 pins, the pins can be used as high-impedance inputs. Port 0 can also be configured to be the multiplexed low-order address/data bus during accesses to external program and data memory. In this mode, P0 has internal pull-ups. 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 bidirectional I/O port with internal pull-ups. 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 pull-ups and can be used as inputs. As inputs, Port 1 pins that are externally being pulled low will source current (IIL) because of the internal pull-ups.

 PORT 2: 

                        Port 2 is an 8-bit bidirectional I/O port with internal pull-ups. 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 pull-ups. Port 2 emits the high-order address byte during fetches from external program memory and during accesses to external data memory that uses 16-bit addresses (MOVX @ DPTR). In this application, Port 2 uses strong internal pull-ups when emitting 1s. During accesses to external data memory that uses 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 bidirectional I/O port with internal pull-ups. 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 pull-ups and can be used as inputs. As inputs, Port 3 pins that are externally being pulled low will source current (IIL) because of the pull-ups. Port 3 receives some control signals for Flash programming and verification. Port 3 also serves the functions of various special features of the 8051.

  

 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)

 RST:

                     Reset input. A high on this pin for two machine cycles while the oscillator is running resets the device. This pin drives high for 98 oscillator periods after the Watchdog times out. The DISRTO bit in SFR AUXR (address 8EH) can be used to disable this feature. In the default state of bit DISRTO, the RESET HIGH out feature is enabled.

 ALE/PROG: 

                     Address Latch Enable (ALE) is an output pulse for latching the low byte of the address during accesses to external memory. This pin is also the program pulse input (PROG) during Flash programming. In normal operation, ALE is emitted at a constant rate of 1/6 the oscillator frequency and may be used for external timing or clocking purposes. Note, however, that one ALE pulse is skipped during each access to external data memory. If desired, ALE operation can be disabled by setting bit 0 of SFR location 8EH. With the bit set, ALE is active only during a MOVX or MOVC instruction. Otherwise, the pin is weakly pulled high. Setting the ALE-disable bit has no effect if the microcontroller is in external execution mode.

PSEN: 

                     Program Store Enable (PSEN) is the read strobe to external program memory. When the AT89S52 is executing code from external program memory, PSEN is activated twice each machine cycle, except that two PSEN activations are skipped during each access to external data memory.

 EA/VPP: 

                     External Access Enable. (EA) must be strapped to GND in order to enable the device to fetch code from external program memory locations starting at 0000H up to FFFFH. Note, however, that if lock bit 1 is programmed, EA will be internally latched on reset. EA should be strapped to VCC for internal program executions. This pin also receives the 12-volt programming enable voltage (VPP) during Flash programming.

 XTAL1:

                      Input to the inverting oscillator amplifier and input to the internal clock operating circuit.

 XTAL2:

                     Output from the inverting oscillator amplifier.