8051 microcontroller and it’s interface

The microprocessor is the core of computer systems.
Nowadays many communication, digital entertainment, portable devices, are controlled by them.
A designer should know what types of components he needs, ways to reduce production costs and product reliable.

1. Gandhinagar Institute Of
Technology
Subject – Microprocessor & Microcontroller
Interfacing (2150907)
Branch – Electrical
Topic – 8051 microcontroller and It’s Interface

2. Name Enrollment No.
Abhishek Chokshi 140120109005

Himal Desai 140120109008
Harsh Dedakia 140120109012

Guided By – Prof. Supraja Ma’am

3. Why do we need to learn
Microprocessors/controllers?
•The microprocessor is the core of computer systems.
•Nowadays many communication, digital
entertainment, portable devices, are controlled by
them.
•A designer should know what types of components he
needs, ways to reduce production costs and product
reliable.

4. Three criteria in Choosing a
Microcontroller
•meeting the computing needs of the task efficiently and
cost effectively
–speed, the amount of ROM and RAM, the number of I/O ports
and timers, size, packaging, power consumption
–easy to upgrade
–cost per unit
–Noise of environment
•availability of software development tools
–assemblers, debuggers, C compilers, emulator, simulator,
technical support
•wide availability and reliable sources of the
microcontrollers

5. Block Diagram
CPU
Interrupt
Control
OSC
Bus
Control
4k
ROM
Timer 1
Timer 2
Serial
128 bytes
RAM
4 I/O Ports
TXDRXD
External Interrupts
P0 P2 P1 P3
Addr/Data

6. 8051 Internal Block Diagram8051 Internal Block Diagram

7. 8051 Basic Component
•4K bytes internal ROM
•128 bytes internal RAM
•Four 8-bit I/O ports (P0 - P3).
•Two 16-bit timers/counters
•One serial interface
RAM
I/O
Port
Timer
Serial
COM
Port
Microcontroller
CPU
A single chip
ROM

8. 1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
40
39
38
37
36
35
34
33
32
31
30
29
28
27
26
25
24
23
22
21
P1.0
P1.1
P1.2
P1.3
P1.4
P1.5
P1.6
P1.7
RST
(RXD)P3.0
(TXD)P3.1
(T0)P3.4
(T1)P3.5
XTAL2
XTAL1
GND
(INT0)P3.2
(INT1)P3.3
(RD)P3.7
(WR)P3.6
Vcc
P0.0(AD0
)P0.1(AD1)
P0.2(AD2
)P0.3(AD3)
P0.4(AD4)
P0.5(AD5)
P0.6(AD6)
P0.7(AD7)
EA/VPP
ALE/PROG
PSEN
P2.7(A15)
P2.6(A14
)P2.5(A13
)P2.4(A12
)P2.3(A11
)P2.2(A10)
P2.1(A9)
P2.0(A8)
8051
(8031)
(8751)
(8951)

9. Port 0（pins 32-39）
•When connecting an 8051 to an external memory, the 8051 uses
ports to send addresses and read instructions.
–16-bit address：P0 provides both address A0-A7, P2
provides address A8-A15.
–Also, P0 provides data lines D0-D7.
•When P0 is used for address/data multiplexing, it is connected to
the 74LS373 to latch the address.
I/O Port Programming
Pins of 8051

10. Port 2 (pins 21 through 28)
•Port 2 occupies a total of 8 pins.
•It can be used as input or output.
•Port 2 does not need any pull-up resistors since it already has
pull-up resistors internally.
•Upon reset, port 2 is configured as an input port.
Port 1 is denoted by P1.
P1.0 ~ P1.7
P1 as an output port (i.e., write CPU data to the external pin)
P1 as an input port (i.e., read pin data into CPU bus)
Port 1（pins 1-8）

11. Port 3（pins 10-17）
•Although port 3 is configured as an output port upon reset,
this is not the way it is most commonly used.
•Port 3 has the additional function of providing signals.
–Serial communications signal：RxD, TxD
–External interrupt：/INT0, /INT1
–Timer/counter：T0, T1
–External memory accesses ：/WR, /RD

12. •Vcc（pin 40）：
–Vcc provides supply voltage to the chip.
–The voltage source is +5V.
•GND（pin 20）：ground
•XTAL1 and XTAL2（pins 19,18）：
–These 2 pins provide external clock.
•RST（pin 9）：reset
–It is an input pin and is active high（normally low）.
•Upon applying a high pulse to RST, the microcontroller will reset
and all values in registers will be lost.

13. •/EA（pin 31）：external access
–The /EA pin is connected to GND to indicate the code is stored
externally.
–For 8051, /EA pin is connected to Vcc.
–“/” means active low.
•/PSEN（pin 29）：program store enable
–This is an output pin and is connected to the OE pin of the ROM
•ALE（pin 30）：address latch enable
–It is an output pin and is active high.
–8051 port 0 provides both address and data.
–The ALE pin is used for de-multiplexing the address and data by
connecting to the G pin of the 74LS373 latch.
•I/O port pins
–The four ports P0, P1, P2, and P3.
–Each port uses 8 pins.
–All I/O pins are bi-directional.

15. •They are both 16 bit registers.
•Each is to hold the address of a byte in memory
•PC contains the address of the next instruction to be
executed.
•DPTR is made up of two 8 bit register DPH and DPL;
•DPTR contains the address of internal & external code and
data that has to be accessed.
Program Counter & Data Pointer

16. A and B CPU registers
•Totally 34 general purpose registers or working registers.
•Two of these A and B hold results of many instructions,
particularly math and logical operations of 8051 cpu.
•The other 32 are in four banks,B0 – B3 of eight registers each.
•A(accumulator) is used for
addition,subtraction,mul,div,boolean bit manipulation and for
data transfers.
•But B register can only be used for mul and div operations.

17. Stack Pointer
•The register used to access
the stack is called SP (stack
pointer) register.
•The stack pointer in the
8051 is only 8 bits wide,
which means that it can take
value 00 to FFH. When
8051 powered up, the SP
register contains value 07.
7FH
30H
2FH
20H
1FH
17H
10H
0FH
07H
08H
18H
00H
Register Bank 0
)Stack) Register Bank 1
Register Bank 2
Register Bank 3
Bit-Addressable RAM
Scratch pad RAM

18. PSW (program status word) register

19. Instruction Timing
•One “machine cycle” = 6 states (S1 - S6)
•One state = 2 clock cycles
–One “machine cycle” = 12 clock cycles
•Instructions take 1 - 4 cycles
–e.g. 1 cycle instructions: ADD, MOV, SETB, NOP
–e.g. 2 cycle instructions: JMP, JZ
–4 cycle instructions: MUL, DIV

21. •RAM memory space allocation in the 8051
7FH
30H
2FH
20H
1FH
17H
10H
0FH
07H
08H
18H
00H
Register Bank 0
)Stack) Register Bank 1
Register Bank 2
Register Bank 3
Bit-Addressable RAM
Scratch pad RAM
Memory Organization

22. Address Multiplexing
for External Memory
Accessing external code memory

23. Accessing External
Data Memory
Interface to 1K RAM

24. Timers/Counters
•A timer is a counter that is increased
with every time an instruction is
executed e.g. 8051 with 12MHz
increases a counter every 1.000 µs
•General 8051 has 3 timer:
–2 16-bit timer
–1 16-bit timer with extra-
functionality (introduced with
the 8052)
Timer/Counter Mode Control Register TMOD
Timer/Counter Control Register TCON

25. Uses of Timers & Counters
- Interval Timing
- Periodic event timing
- Time base for measurements
- Event Counting
-Baud Rate Generation
8051 Timers
- 2 timers (Timer 0 and Timer 1)
- 16-bit timers (65,535) max
- Flag is set when the timer overflows
-Timers can be based on internal clock (OSC/6) or from
external source (counter mode).
TMOD - Timer/Counter mode register
TCON - Timer/Counter control register

26. TMOD Register:
•Gate : When set, timer only runs while INT(0,1) is high.
•C/T : Counter/Timer select bit.
•M1 : Mode bit 1.
•M0 : Mode bit 0.

27. TCON Register:
•TF1: Timer 1 overflow flag.TR1: Timer 1 run control bit.
•TF0: Timer 0 overflag. TR0: Timer 0 run control bit.
•IE1: External interrupt 1 edge flag. IT1: External interrupt 1 type flag.
•IE0: External interrupt 0 edge flag. IT0: External interrupt 0 type flag.
•TF: Overflow flag
–Set by hardware on Timer/Counter overflow
–Cleared by hardware when processor vectors to interrupt routine
•TR: Run control bit
–Set/Cleared by software to turn Timer/Counter on/off
•IE: Interrupt Edge flag
–Set by hardware when external interrupt edge detected
–Cleared when interrupt processed
•IT: Interrupt Type control bit
–Set/Cleared by software to specify
falling edge/low level triggered external interrupts

28. Timer Modes
Mode 0: 13-Bit Timer
- Lower byte (TL0/TL1) + 5 bits of upper bytes (TH0/TH1).
- Backward compatible to the 8048
- Not generally used

29. Mode 1: 16-bit
- All 16 bits of the timer (TH0/TL0, TH1,TL1) are used.
- Maximum count is 65,536
-At 12Mhz, maximum interval is 65536 microseconds
or 65.536 milliseconds
- TF0 must be reset after each overflow
- THx / TLx must be manually reloaded after each overflow.
Mode 2: 8-bit Auto Reload
- Only the lower byte (TLx) is used for counting.
- Upper byte (THx) holds the value to reload into TLx after
an overflow.
- TFx must be manually cleared.
- Maximum count is 256
- Maximum interval is 256 Microseconds or .256
milliseconds

30. Mode 3- Split Timer
- Splits Timer 0 into two
8-bit timers
- TL0 sets TF0
- TH0 sets TF1
- Timer 1 is available for
other 3 modes, but the
TF1 is not available.

31. Advantages of Microcontroller based
System
•As the peripherals are integrated into a single chip, the overall system
cost is very less
•The product is of small size compared to micro processor based system
•The system design now requires very little efforts
•As the peripherals are integrated with a microprocessor the system is
more reliable
•Though microcontroller may have on chip ROM,RAM and I/O ports,
addition ROM, RAM I/O ports may be interfaced externally if required
•On chip ROM provide a software security

32. Disadvantages of microprocessor
•The overall system cost is high
•A large sized PCB is required for assembling all the components
•Overall product design requires more time
•Physical size of the product is big
•A discrete components are used, the system is not reliable

33. Edsim51 Simulator diagram

34. References
•www.wikipedia.org
•https://iitg.vlab.co.in/
•https://coep.vlab.co.in/
•https://www.youtube.com/watch?v=95uGOJ1Ud2c&list=PLJGA4olwzpA-rvcdWULcRuMn2495g0n8j
•Techmax Publication