8051 pin diagram with functions

1. Course Name: MICROCONTROLLER
Course Code: BEC405A
1

2. 1.7 Pin diagram of 8051Microcontroller
• Pins 1 to 8 (Port 1): These pins are a bi-directional I/O port that can be
used for interfacing with external devices.
• Pin 9 (RESET): This pin is used to reset the microcontroller to its initial
values.
• Pins 10 to 17 (Port 3): These pins have multiple functions including
serving as interrupt inputs, timer inputs, control signals, and serial
communication signals.
• Pins 18 & 19 (XTAL1 & XTAL2): These pins are used for connecting an
external crystal oscillator that provides the clock signal for the
microcontroller.
• Pin 20 (GND): This pin is the ground connection for the microcontroller.
• Pin 21 to 28 (Port 2): These pins are another bi-directional I/O port that
can be used for various purposes.
• Pin 29 (PSEN): This pin is the Program Store Enable signal and is used
during the process of fetching instructions from program memory.
• Pin 30(ALE) − This is ALE pin which stands for Address Latch Enable. It
is used to demultiplex the address-data signal of port.
• Pin 31 (EA): This pin is the External Access input and is used to enable
or disable external memory interfacing.
• Pins 32 to 39 (Port 0): This is a bi-directional I/O port that also serves as
the lower order address bus for memory access.
• Pin 40(VCC): This pin provides the power supply voltage (typically +5V)
to the microcontroller.

3. 8051 CONNECTED TO 12MHZ CRYSTAL
AND RESET CIRCUIT

4. 1.7 Pin diagram of 8051Microcontroller​

5. Ceramic oscillator-low cost but frequency stability and
accuracy is less compare to crystal oscillator.
Smallest time in μC is pulse. This Smallest time
accomplishes any simple instruction/complex instruction.


2 pulses=1 state(sub operations: fetch/ decode/ execute/

write data)
6 states=12 clock cycles= 1 machine cycle
Any instruction execution time is


C= no. of machine cycles 8051 instruction uses.
Crystal frequency:11.0592 M Hz to support for
different baud rates.



6. 1.9 Internal Memory organization of 8051 Microcontroller
Program Memory (ROM):
 On-chip, typically 4KB in older models, though variants can have
more.
 Stores the program instructions that the microcontroller executes.
 Not directly writable by the user program. The program is written
into ROM during the manufacturing process or through special
programming techniques.
Data Memory (RAM):
 On-chip, usually 128 bytes (though some variants may have more).
 Stores temporary data used during program execution, such as
variables, intermediate results, and stack data.
 Accessible by the user program for reading, writing, and
manipulation.
Internal RAM Organization:
 The 128 bytes of internal data memory are further divided into two
sections:
Special Function Registers (SFRs):
 Occupy the lower address range (typically 00h to 1Fh).
 Each SFR is a small memory location (usually 8-bit) that controls
various functionalities of the microcontroller.

7. 1.8 I/O ports functions in 8051 Microcontroller

8. 1.8 I/O ports functions in 8051 Microcontroller
• Pin configuration, i.e. the pin can be configured as 1 for input and 0 for
output as per the logic state.
• Input/Output (I/O) pin − All the circuits within the microcontroller must
be connected to one of its pins except P0 port because it does not
have pull-up resistors built-in.
• Input pin − Logic 1 is applied to a bit of the P register. The output FE
transistor is turned off and the other pin remains connected to the
power supply voltage over a pull-up resistor of high resistance.

9. 1.10 External Memory (ROM & RAM) interfacing 8051 Microcontroller
1.10.1 External ROM (Program Memory) Interfacing
 Port 0 is used as multiplexed data & address lines. It
gives lower order (A7-A0) 8-bit address in initial T
cycle & higher order (A8-A15) used as data bus.
 8-bit address is latched using external latch & ALE
signal from 8051.
 Port 2 provides higher order (A15-A8) 8-bit address.
 PSEN is used to activate the output enable signal of
external ROM/EPROM.
1.10.2 External RAM (Data Memory) Interfacing
 Port 0 is used as multiplexed data & address lines.
 Address lines are decoded using external latch &
ALE signal from 8051 to provide lower order (A7-
A0) address lines.
 Port 2 gives higher order address lines.
 RD & WR signals from 8051 selects the memory
read & memory write operations respectively.
Example Code:
 To read instructions from the external ROM, you can use the MOVX instruction in
your 8051-assembly code:
MOVX A, @DPTR ; Read data from external ROM into accumulator
Example Code:
 To read data from and write data to the external RAM, you can use the MOVX
instruction in your 8051-assembly code:
MOVX A, @DPTR ; Read data from external RAM into
accumulator
MOVX @DPTR, A ; Write data from accumulator to external
RAM

10. THANK YOU