C o n t e n t s
- What is a microcontroller ?
- Different Addressing Modes of microcontroller
- 8051 microcontroller PIN Diagram
- 8051 microcontroller Architecture
- Memory of 8051
- Interrupts of 8051
- Features of a microcontroller
- Microprocessor vs Microcontroller
What is a Microcontroller?
“A microcontroller is a small computer that consists of processor, internal RAM, ROM or flash, timers, interrupt handler, serial interface, ports & other application-specific devices.”
- A microcontroller is employed if the memory prerequisite for computations is small and the programs and ports are used for the control and communication purpose.
- For example i.e., 8051, PIC and ARM are the standard Microcontrollers.
Main Features of 8051 Microcontroller :
- 8-bit ALU and Accumulator, 8 bit registers, 8 bit data bus and 2×16 bit address bus/program counter/data pointer and related 8/11/16 bit operations.
- Fast interrupt with operational register.
- Power saving mode.
Addressing Mode of 8051 Microcontroller:
“An addressing mode denotes by what method addressing a particular memory location.”
There are five important addressing modes in 8051 microcontroller, they are:
Each of these addressing modes provide important flexibility.
Immediate addressing is like the data to be stored in memory instantly as per the opcode . The instruction itself commands which value might be kept in memories specifically.
E.g., the instruction as follows:
MOV A, #20H
Here memonics utilizes immediate addressing for the reason that the accumulator is going to be filled with the value which mentioned.
In direct addressing, the value to be loaded is time dependent, this adressing certainly not flexible.
Indirect addressing is a really good comparatively that in most instances contributes an exceptional degree of flexibility. This is by only means to get the additional 128 bytes of internal RAM located in an 8051. Example is like
MOV A, @R0
This instruction bases the 8051 Microcontroller to have another look at the value of the R0 register. The 8051 will then load the accumulator with the info of internal RAM that’s located at the address indicated by R0 register.
By way of instance, let us say R0 retains the value 50H and address 50H retains the value 66H. When the above-mentioned instruction is implemented the 8051 will assess the value of R0. Since R0 retains 50H, the 8051 will find the value of this internal RAM address 50H and keep it in the accumulator. Indirect addressing consistently identifies internal RAM; it refers to a SFR
External memory is get into by means of a set of instructions uses ‘external direct’ addressing. There are two such types of commands that could be used for external direct addressing operations, those are
MOVX A, @DPTR
MOVX @DPTR, A
Here, the two controls use DPTR. In these commands, DPTR should first be loaded using the location of external memory which is to be read or write. After DPTR retains the proper external memory card, the initial command will transfer the contents of the external memory address to the accumulator. The next command is going to do the contrary; it permits to write the accumulator’s value to the external memory address which is already pointed by DPTR.
External memory may be acquired using a indirect addressing that is known as external indirect addressing. This kind of addressing is generally utilized in relatively minor tasks which have a rather modest number of external RAM. Such example is
MOVX @R0, A
The value of R0 has to be read and the value of the accumulator is from external RAM location. Considering that the value of R0 could simply be 00 through FFh, and is limited to 256 bytes. Employing external indirect addressing; nonetheless, it’s normally simpler to use external direct mode if the task has more than 256 bytes.
Architecture of 8051 Microcontroller:
- 8051 is equipped with an 8-bit CPU with a Boolean processor.
- 5 interrupts. 2 Externals, 2 priority levels.
- This has two sixteen bit timer/counters.
- One programmable full-duplex serial port.
- Total 32 I/O lines.
- Equipped with the 4 KB of on-chip ROM ; EPROM is also available in some models.
- 128 bytes of on-chip RAM, just enough for many single chip.
PIN Diagram of 8051 Microcontroller:
8051 Microcontroller PIN Configuration:
PIN 1 to 8
These pins generaly utilized as I/P or O/P according to the user requirements.
This is utilized as Resetting purpose; Generally HL signal pin halts the MCU and clear all the registers. When this pin is back to LO, new program will start.
PIN 10 – 17:
These are utilized as with the port 1, each of these pins could be employed as universal i/p or o/p.
RXD- Ac as a serial I/P for the asynchronous trasfer otherwise clock output for synchronous mode of operation.
TXD- Act as a serial O/P for the asynchronous transfer otherwise clock output for synchronous mode of operation.
INT0- This is for input interrupt 0
INT1- This is for input interrupt 1
T0- This is employed for clock input of the timer 0
T1- This is dedicated for clock input of the timer 1
WR- This is for write operation controlling from external RAM memory device.
RD- This pin is dedicated for read operation to external RAM memory
X2 and X1- These are for input and output operation of the internal oscillator
GND- Ground ; This is for grounding the chip.
Port 2- provisional external memory is not present, Port 2 will work as an universal I/O operation.
PSEN: MCU triggers after reading each byte from the program memory. When an external memory is employed for program storage purpose, then PSEN will be associated with the control operation.
ALE: This will have important function before external memory reading, MCU will send the lower byte of the address registers to the Port-P0 and triggers the output ALE.
EA: The LOW signal refer to the Port- P2 and P3 for transporting addresses irrespective of the memory status.
Port 0: analogous to port 2, pins of port 0 could be utilized as universal I/O. The P0 performs as address O/P if ALE pin is at high state.
VCC:This is for +5V dc power supply.
Interrupts of 8051 microcontroller:
Five interrupts are provided in 8051. Three sets automatically by internal operations and other two is triggered by external signal linked to pins INT0 and INT1.
Automatic interrupts are:
- Timer Flag 0
- Timer Flag 1
- Serial Port Interrupt (R1 or T1)
Interrupt Name Interrupt Address
Timer Flag o 0 0 0 B
Timer Flag 1 0 0 1 B
INT0 0 0 0 3
INT1 0 0 1 3
Serial Input R1/ T1
Applications of Microcontroller:
- Microcontroller is employed in Mobile phones, camera circuitry.
- Microcontrollers are used extensively in Automobile Industry
- Computer Systems like traffic signal controlling.
- Different control operation such as heater, greezer, liftcontrol, Micro-oven etc.
Comparison of Microprocessor vs. Microcontroller:
|CPU||It has 1 Central Processing Unit||It has a Central Processing Unit, Memory, Input-output pins.|
|USE||Microprocessor is used in personal computers.||Microcontroller has applications in embedded system.|
|INTERFACE||Microprocessor interface is complicated.||Simpler Interface|
|COST||They are expensive||They are inexpensive|
|REGISTER||It has less numbers of registers, operations are mostly memory based.||Greater number of registers making it easy for operations.|
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