8051

1. 8051 (MICROCONTROLLER)
Nitin Ahire
XIE, Mahim
Prof. Nitin Ahire
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2. MICROCONTROLLER
What is a microcontroller ?
Basically a device which integrates a number of
components of a microprocessor system on to a
single chip, only need to supplied power and
clocking.
Microcontroller combines on the same chip
1) The CPU core
2) I/O Ports
3) Memory
4) Timer
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3. HISTORY
In 1981, Intel Corporation introduced an 8 bit
microcontroller called 8051.
It was also referred to as “ system on chip”
The 8051 is the original member of MCS-51
family
Other members of 8051
8031, 8052, 8751, AT89C51, etc
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4. Prof. Nitin Ahire
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Microprocessor
CPU is stand-alone, RAM,
ROM, I/O, timer are separate
Designer can decide on the
amount of ROM, RAM and
I/O ports.
Expansive
General-purpose
Microcontroller
• CPU, RAM, ROM, I/O and
timer are all on a single chip
• Fix amount of on-chip ROM,
RAM, I/O ports
• For applications in which cost,
power and space are critical
• Single-purpose
Microprocessor vs. Microcontroller

5. CHOOSING A MICROCONTROLLER
Computing needs
Speed, packaging, power consumption, RAM, ROM,
I/O pins, timers, upgrade to high performance or
low-power versions, cost etc
Software development tools
Assembler, debugger, C compiler, technical support
Availability & source
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6. Prof. Nitin Ahire
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Microcontroller vs.Microcontroller vs.
MicroprocessorsMicroprocessors

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An embedded product uses a microcontroller
(microprocessor) to do one (single) task only.
Embedded system means the processor is
embedded into that application.
In an embedded system, there is only one
application software that is typically burned into
ROM.
Example：printer, keyboard, video game player
Embedded System

8. COMPANIES PRODUCING 8051
Table :Some Companies Producing a Member ofTable :Some Companies Producing a Member ofTable :Some Companies Producing a Member ofTable :Some Companies Producing a Member of
the 8051 Familythe 8051 Familythe 8051 Familythe 8051 Family
Company Web Site
Intel www.intel.com/design/mcs51
Atmel www.atmel.com
Philips/Signetics www.semiconductors.philips.com
Siemens www.sci.siemens.com
Dallas
Semiconductor
www.dalsemi.com
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9. 8051 FAMILY
Table :Comparison of 8051 Family MembersTable :Comparison of 8051 Family MembersTable :Comparison of 8051 Family MembersTable :Comparison of 8051 Family Members
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FeatureFeature 80518051 80528052 80318031
ROM (on chip program space in bytes)ROM (on chip program space in bytes) 4K4K 8K8K 0K0K
RAM (bytes)RAM (bytes) 128128 256256 128128
TimersTimers 22 33 22
I/O pinsI/O pins 3232 3232 3232
Serial portSerial port 11 11 11
Interrupt sourcesInterrupt sources 66 88 66

10. VARIOUS 8051 MICROCONTROLLERS
8031 microcontroller (ROM -Less)
8751 microcontroller
UV-EPROM (20 minutes)
AT89C51 from Atmel Corporation
Flash (erase before write)
DS5000 from Dallas Semiconductor
NV-RAM (changed one byte at a time), RTC (real-time
clock)
OTP (one-time-programmable) version of 8051
8051 family from Philips
AD, DA, extended I/O, OTP and flash
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11. MAJOR 8-BIT MICROCONTROLLERS.
They are : 1)Motorola’s 6811, 2)Intel’s 8051,
3)Zilog Z8, and 4)PIC 16X from Microchip
Technology.
Each of the above microcontrollers has unique
instruction set and register set; there fore they
are not compatible with each other. Program
written for one will not run on the others
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12. FEATURE OF 8051
The 8051 is 8 – bit microcontroller.
There are 16 bit -address lines and 8 –bit data lines.
On chip Program memory
ROM 4 KB
On chip Data memory
RAM 128 byte
32 bidirectional I/O lines arranged as four 8-bit port
( port 0 – port 3)
2- sixteen bit Timer/Counter ( Timer 0 and Timer 1)
Four register Banks ( Bank 0- Bank 3)
Direct bit and byte addressability
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13. INSIDE 8051 MICROCONTROLLER
Introduced by Intel in 1981
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15. ARCHITECTURE OF 8051
Accumulator : It is an 8 – bit register used for
arithmetic and logical operation to
accumulate the result. Several function like
rotate, swap etc apply on the accumulator
B register: It is use with A register for
multiplication and division for other
instruction it is treated as scratch pad
register.
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16. ARCHITECTURE OF 8051
ALU : The ALU can perform arithmetic and
logical operation on 8-bit data. Like add, sub,
mul, div or AND or OR ,compliment, etc.
Program counter (PC) : It is a 16 –bit register. It
is used to hold the address of an instruction
(program) stored in the memory.
Program status word ( PSW ): Many instruction
affect the status flags in order to address these
flags conveniently they can be grouped to from
PSW
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17. 8051 FLAG BITS
PSW (Program status word) register
It is an 8-bit register
It is a bit addressable register
CY- Carry flag PSW.7
AC- Auxiliary carry PSW.6
FO – Available to the user for general purpose
RS0-RS1- Register Bank selector (PSW.3, PSW.4)
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CY AC -OVRS0RS1FO P

18. 8051 FLAG BITS
OV- overflow Flag PSW.2
P- Parity Flag PSW.0
RS1 RS0 Register Bank Address
0 0 Bank 0 00h-07h
0 1 Bank 1 08h- 0fh
1 0 Bank2 10h-17h
1 1 Bank3 18h-1Fh
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19. 8051 FLAG BITS
CY- This flag is set whenever there is carry from d7 bit.
This flag bit is affected after addition or subtraction. It
can also set 1 or 0 directly by instruction such as
“SETB C” and “ CLR C”
AC- If there is carry from D3 to D4 during an ADD or
SUB operation, this bit is set; otherwise it is cleared
( used in BCD arithmetic)
P – The Parity Flag reflects the number of 1s in the A
( accumulator) . If A contains odd number of 1s, then
P=1 and A contains even number of 1s, then P=0
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20. 8051 FLAG BITS
OV – this flag is set whenever the result of
singed number operation is too large, causing
the high-order bit to overflow into the sign bit
( It is used only in signed operation)
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21. 8051 REGISTER BANKS AND STACK
The 8051 has a total 128 bytes of RAM.
The 128 bytes of RAM in side the 8051 are
assigned address 00 to 7Fh.
The 128 bytes are divided into three different
groups as follows
1) A total of 32323232 bytes from locations 00 to 1F00 to 1F00 to 1F00 to 1F hex
are set aside for register banks and the stack.
2) A total of 16161616 bytes from locations 20h to 2Fh20h to 2Fh20h to 2Fh20h to 2Fh
are aside for bit addressable read/write memory
3) A total 80808080 bytes from location 30h to 7Fh30h to 7Fh30h to 7Fh30h to 7Fh are
used for read and write storage normally called
‘scratch pad’ RAM
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22. RAM memory space allocation in theRAM memory space allocation in theRAM memory space allocation in theRAM memory space allocation in the 8051805180518051
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7FH
30H
2FH
20H
1FH
17H
10H
0FH
07H
08H
18H
00H Register Bank 0
Register Bank 1
Register Bank 2
Register Bank 3
Bit-Addressable RAM
Scratch pad RAM

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Bank 0
Bank 2
Bank 1
Bank 3
0001020304050607
08090A0B0C0D0E0F
78797A7B7C7D7E7F
00
1F
20
2F
30
7F
4 Reg. BANK 8 bytes each
32 bytes
Bit addressable RAM
16 bytes ( 80 bits)
General purpose RAM
80 bytes
Internal RAM memory organization

24. REGISTER BANKS IN 8051
The 32 bytes of RAM are divided into 4 banks
of register in which each bank has 8 registers,
R0-R7. Bank 0 Bank 1 Bank 2
Bank3
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R7
R6
R5
R4
R3
R2
R1
R0
R7
R6
R5
R4
R3
R2
R1
R0
R7
R6
R5
R4
R3
R2
R1
R0
R7
R6
R5
R4
R3
R2
R1
R0

25. STACK IN THE 8051
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.
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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

26. ARCHITECTURE OF 8051
DPTR: The data pointer is 16 bit register
It is used to hold the address of data in the
memory.
It can be accessed separately as lower
8 bit (DPL) and higher 8 bit (DPH)
The DPTR does not have a single internal
address instead DPH and DPL are each
assigned a separate address.
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27. ARCHITECTURE OF 8051
Stack and Stack Pointer :
The stack is the reserved area of the memory in the
RAM where temporary information may be stored.
an 8 – bit stack pointer is used to hold the address
of most recent stack entry. Generally it is called top
of the stack
It work on LIFO or FILO principle
By default location of stack pointer is 07h
we can change the default location by MOV SP,# XX
h
( RAM location 30h – 7Fh)
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28. ARCHITECTURE OF 8051
SFR (Special Function Registers) :
SFR registers are placed in the address space
immediately above the 128 bytes of RAM,
from address 80h to FF h
The SFR memory consists of important
registers like A,B,PSW,PCON,TCON,TMOD etc
some registers are bit addressable while
remaining are byte addressable.
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29. SFR (SPECIAL FUNCTION REGISTERS)
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30. ARCHITECTURE OF 8051
Some of the address i.e. locations in between
80h to FF h are not used if we try to used, then
we may get the unpredictable result like data
lost
The PC is not the part of SFR the PC does not
have an internal RAM address.
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31. Prof. Nitin Ahire
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A
80
81
82
87
90
FF
F0
E0
83
B
P0
SP
DPL
DPH
PCON
P1
PSWD0
Address SFR Registers
d7d5 d5 d4 d3 d2 d1d0
d7d5 d5 d4 d3 d2 d1d0

32. HOW STACK ARE ACCESSED IN THE 8051
Pushing data on to the stack
Show the stack and stack pointer for the following
Assume default stack area
MOV R6,#25H ; copy number 25 in R6
MOV R1,#12H ; copy number 12 in R1
MOV R4,#0F3H ; copy number F3 in R4
PUSH 6
PUSH 1
PUSH 4
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33. PUSH & POP
Solution:
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08
09
0A
0B
Start SP = 07
2508
09
0A
0B
SP = 08
25
12
08
09
0A
0B
SP = 09
25
F3
12
08
09
0A
0B
SP = 0A
After PUSH 6 After PUSH 1 After PUSH 4

34. PUSH & POP
Popping from the stack
Examining the stack, show the content of the
registers and SP after execution of the following
instruction
POP 3 ; POP stack into R3
POP 5 ; POP stack into R5
POP 2 ;POP stack into R2
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35. PUSH & POP
Solutions
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6C
54
F9
76
08
09
0A
0B
Start SP = 0B
6C
F9
76
08
09
0A
0B
SP = 0A
6C
76
08
09
0A
0B
SP = 09
6C08
09
0A
0B
SP = 08
R3=54
After POP 5 After POP 2
After POP 3
R5=F9 R2=76

36. PIN DESCRIPTION OF THE 8051
8051 family members come in different
package, such as DIP (dual in line package),
QFP (quad flat package), and LLC (leadless chip
carrier)
Some companies provide a 20 pin version of
8051 with reduced numbers of I/O ports
Majority of developers use the 40-pin DIP
package chip.
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37. Prof. Nitin Ahire
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Pin Description of thePin Description of the 80518051
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)

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Figure (a). XTAL Connection toFigure (a). XTAL Connection to 80518051
C2
30pF
C1
30pF
XTAL2
XTAL1
GND
Using a quartz crystal oscillator ( operating freq range 1MHZ to 16 MHZ )
We can observe the frequency on the XTAL2 pin.

39. PINS OF 8051（2/4）
RST（pin 9） Reset
It is an input pin and is active high（ normally low）
The high pulse must be high at least 2 machine cycles.
If crystal freq=16 Mhz then find the machine cycle
sol: 16MHz/12=1.33MHz
MC = 1/ 1.33Mhz =0.75 microsec
If crystal freq=11.0592 Mhz then find the machine
cycle
sol: 11.0592MHz/12=921.6KHz
MC = 1/ 921.6Khz =1.085 microsec
Time to execute one cycle instruction e.g. ADD A,R1
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40. It is a power-on reset.
Upon applying a high pulse to RST, the
microcontroller will reset and all values in registers
will be lost.
Reset values of some 8051 registers
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41. RegisterRegister Reset valueReset value
PCPC 00000000
ACCACC 0000
BB 0000
PSWPSW 0000
SPSP 0707
DTPRDTPR 00000000
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42. FIGURE. RESET WITH DEBOUNCE CIRCUIT
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30 pF
30 pF
8.2 K
10 uF
+
Vcc
11.0592 MHz
EA/VPP
X1
X2
RST
31
19
18
9

43. PINS OF 8051（3/4）
/EA pin 31）external access
There is no on-chip ROM in 8031 and 8032 .
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 external ROM.
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44. PINS OF 8051（4/4）
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..
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45. PINS OF I/O PORT
The 8051 has four I/O ports
Port 0 （pins 32-39） ：P0（P0.0～ to P0.7）
Port 1（pins 1-8） ：P1（P1.0～ to P1.7）
Port 2（pins 21-28） ：P2（P2.0～ to P2.7）
Port 3（pins 10-17） ：P3（P3.0～ to P3.7）
Each port has 8 pins.
Named P0.X （X=0,1,...,7）, P1.X, P2.X, P3.X
P0.0 is the bit 0（LSB）of P0
P0.7 is the bit 7（MSB）of P0
These 8 bits form a byte.
Each port can be used as input or output (bi-direction).
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46. Prof. Nitin Ahire
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A Pin of PortA Pin of Port 00
8051 IC
D Q
Clk Q
Read latch
Read pin
Write to latch
Internal CPU
bus
M1
P0.X
pinP1.X
TB1
TB2
P1.x

47. PORT 0 WITH PULL-UP RESISTORS
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P0.0
P0.1
P0.2
P0.3
P0.4
P0.5
P0.6
P0.7
DS5000
8751
8951
Vcc
10 K
Port
0

48. PORT 3 ALTERNATE FUNCTIONS
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1717RDRDPP33..77
1616WRWRPP33..66
1515TT11PP33..55
1414TT00PP33..44
1313INTINT11PP33..33
1212INTINT00P3.2P3.2
1111TxDTxDPP33..11
1010RxDRxDPP33..00
PinPinFunctionFunctionPP33 BitBit
