The document discusses the 8051 microcontroller. It begins with an introduction and table of contents. It then provides details about the 8051 including its block diagram, pin descriptions and functions, memory mapping, registers, stack, I/O port programming, timers, and interrupts.

1. MICROCONTROLLER 8051
Presented ByMUKESH KUMAR KASHYAP
Roll No-3352808033
&
SHRI SHANKARACHARYA INSTITUTE OF TECHNOLGY
MANAGEMENT,BHILAI

2. Contents:
Introduction
Block Diagram and Pin Description of the 8051
Registers
Memory mapping in 8051
Stack in the 8051
I/O Port Programming
Timer
Interrupt
2

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.
3

4. Different aspects of a microprocessor/controller
Hardware :Interface to the real world
Software :order how to deal with inputs
4

5. The necessary tools for a
microprocessor/controller
CPU: Central Processing Unit
I/O: Input /Output
Bus: Address bus & Data bus
Memory: RAM & ROM
Timer
Interrupt
Serial Port
Parallel Port
5

6. Microprocessors:
General-purpose microprocessor
 CPU for Computers
 No RAM, ROM, I/O on CPU chip itself
 Example ： Intel’s x86, Motorola’s 680x0
CPU
GeneralPurpose
Microprocessor
Many chips on mother’s board
Data Bus
RAM
ROM
I/O
Port
Address Bus
General-Purpose Microprocessor System
6
Timer
Serial
COM
Port

7. Microcontroller :
 A smaller computer
 On-chip RAM, ROM, I/O ports...
 Example ： Motorola’s 6811, Intel’s 8051, Zilog’s Z8 and PIC 16X
CPU
I/O
Port
7
RAM ROM
Serial
Timer COM
Port
A single chip
Microcontroller

8. Microprocessor vs. Microcontroller
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
 versatility
 general-purpose
8
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

9. Embedded System
 Embedded system means the processor is embedded into that
application.
 An embedded product uses a microprocessor or microcontroller
to do one task only.
 In an embedded system, there is only one application software
that is typically burned into ROM.
 Example ： printer, keyboard, video game player
9

10. Three criteria in Choosing a Microcontroller
1.
1.
1.
10
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
availability of software development tools
•
assemblers, debuggers, C compilers, emulator, simulator,
technical support
wide availability and reliable sources of the microcontrollers.

11. Comparison of the 8051 Family Members
89XX
ROM
RAM
Timer
Int
IO pin
Other
8951
4k
128
2
Source
6
32
-
8952
8k
256
3
8
32
-
8953
12k
256
3
9
32
WD
8955
20k
256
3
8
32
WD
898252
8k
256
3
9
32
ISP
891051
1k
64
1
3
16
AC
892051
2k
128
2
6
16
AC
WD: Watch Dog Timer
AC: Analog Comparator
ISP: In System Programmable
11

12. Block Diagram
External interrupts
Interrupt
Control
On-chip
ROM for
program
code
Timer/Counter
On-chip
RAM
Timer 1
Timer 0
CPU
OSC
Bus
Control
4 I/O Ports
P0 P1 P2 P3
Address/Data
12
Serial
Port
TxD RxD
Counter
Inputs

13. 13

14. Pin Description of the 8051
P1.0
P1.1
P1.2
P1.3
P1.4
P1.5
P1.6
P1.7
RST
(RXD)P3.0
(TXD)P3.1
(INT0)P3.2
(INT1)P3.3
(T0)P3.4
(T1)P3.5
(WR)P3.6
(RD)P3.7
XTAL2
XTAL1
GND
14
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
8051
(8031)
40
39
38
37
36
35
34
33
32
31
30
29
28
27
26
25
24
23
22
21
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
P
) 2.5(A13
P2.4(A12
)
P
) 2.3(A11
P2.2(A10)
)
P2.1(A9)
P2.0(A8)

15. Pins of 8051 （ 1/4 ）
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 ）
15

16. XTAL Connection to 8051
 Using a quartz crystal oscillator
 We can observe the frequency on the XTAL2 pin.
C2
XTAL2
30pF
C1
XTAL1
30pF
GND
16

17. 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.
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
17

18. Power-On RESET Circuit
Vcc
+
10 uF
31
30 pF
8.2 K
30 pF
11.0592 MHz
19
18
EA/VPP
X1
X2
9 RST
18

19. 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.
/PSEN ＆ ALE are used for external ROM.
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.
19

20. 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.
20

21. Pins of I/O Port
The 8051 has four I/O ports
Port 0 （ pins 32-39 ）： P0 （ P0.0 ～ P0.7 ）
Port 1 （ pins 1-8 ） ： P1 （ P1.0 ～ P1.7 ）
Port 2 （ pins 21-28 ）： P2 （ P2.0 ～ P2.7 ）
Port 3 （ pins 10-17 ）： P3 （ P3.0 ～ P3.7 ）
Each port has 8 pins.
Named P0.X （ X=0,1,...,7 ） , P1.X, P2.X, P3.X
Ex ： P0.0 is the bit 0 （ LSB ） of P0
Ex ： 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).
21

22. Hardware Structure of I/O Pin
 Each pin of I/O ports
 Internal CPU bus ： communicate with CPU
 A D latch store the value of this pin
 D latch is controlled by “Write to latch”
to latch ＝ 1 ： write data into the D latch
 2 Tri-state buffer :
 TB1: controlled by “Read pin”
 Read pin ＝ 1 ： really read the data present at the pin
 TB2: controlled by “Read latch”
 Read latch ＝ 1 ： read value from internal latch
 A transistor M1 gate
 Gate=0: open
 Gate=1: close
 Write
22

23. D Latch:
23

24. A Pin of Port 1
Read latch
TB2
Vcc
Load(L1)
Internal CPU
bus
D
Write to latch
Clk
P1.X
pin
Q
P1.X
Q
M1
TB1
Read pin
24
8051 IC

25. Writing “1” to Output Pin P1.X
Read latch
Vcc
TB2
Load(L1) 2. output pin is
Vcc
1. write a 1 to the pin
Internal CPU
bus
D
Write to latch
Clk
1
Q
P1.X
pin
P1.X
Q
0
M1
TB1
Read pin
25
8051 IC
output 1

26. Writing “0” to Output Pin P1.X
Read latch
Vcc
TB2
Load(L1) 2. output pin is
ground
1. write a 0 to the pin
Internal CPU
bus
D
Write to latch
Clk
0
Q
P1.X
pin
P1.X
Q
1
M1
TB1
Read pin
26
8051 IC
output 0

27. Reading “High” at Input Pin
Read latch
1.
TB2
write a 1 to the pin MOV
P1,#0FFH
Internal CPU bus
2. MOV A,P1
Vcc
external pin=High
Load(L1)
D
1
Q
1
P1.X
Write to latch
Clk
0
Q
M1
TB1
Read pin
3. Read pin=1 Read latch=0
Write to latch=1
27
8051 IC
P1.X pin

28. Reading “Low” at Input Pin
Read latch
1.
Vcc
2. MOV A,P1
TB2
write a 1 to the pin
Load(L1)
external pin=Low
MOV P1,#0FFH
Internal CPU bus
D
1
Q
0
P1.X
Write to latch
Clk
Q
0
M1
TB1
Read pin
3. Read pin=1 Read latch=0
Write to latch=1
28
8051 IC
P1.X pin

29. Other Pins
P1, P2, and P3 have internal pull-up resisters.
P1, P2, and P3 are not open drain.
P0 has no internal pull-up resistors and does not
connects to Vcc inside the 8051.
P0 is open drain.
Compare the figures of P1.X and P0.X.
However, for a programmer, it is the same to
program P0, P1, P2 and P3.
All the ports upon RESET are configured as
output.
29

30. A Pin of Port 0
Read latch
TB2
Internal CPU
bus
D
Write to latch
Clk
P0.X
pin
Q
P1.X
Q
M1
TB1
Read pin
30
8051 IC

31. Port 0 with Pull-Up Resistors
Vcc
31
Port 0
P0.0
DS5000 P0.1
P0.2
8751
P0.3
P0.4
8951
P0.5
P0.6
P0.7
10 K

32. Port 3 Alternate Functions
P3 Bit
Pin
P3.0
P3.1
P3.2
P3.3
P3.4
P3.5
P3.6
P3.7
32
Function
RxD
TxD
INT0
INT1
T0
T1
WR
RD
10
11
12
13
14
15
16
17

33. RESET Value of Some 8051 Registers:
Register
PC
ACC
B
PSW
SP
DPTR
RAM are all zero.
33
Reset Value
0000
0000
0000
0000
0007
0000

34. Registers
A
B
R0
DPTR
DPH
DPL
R1
R2
PC
PC
R3
R4
R5
R6
R7
Some 8-bitt Registers of
the 8051
34
Some 8051 16-bit Register

35. Memory mapping in 8051
ROM memory map in 8051 family
4k
0000H
8k
32k
0000H
0000H
0FFFH
DS5000-32
8751
AT89C51
1FFFH
from Atmel Corporation
35
8752
AT89C52
7FFFH
from Dallas Semiconductor

36. RAM memory space allocation in the 8051
7FH
Scratch pad RAM
30H
2FH
Bit-Addressable RAM
20H
1FH
18H
17H
10H
0FH
08H
07H
00H
36
Register Bank 3
Register Bank 2
Stack) Register Bank 1)
Register Bank 0

37. Stack in the 8051
 The register used to access the
stack is called SP (stack
pointer) register.
7FH
Scratch pad RAM
30H
 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.
37
2FH
Bit-Addressable RAM
20H
1FH
18H
17H
10H
0FH
08H
07H
00H
Register Bank 3
Register Bank 2
Stack) Register Bank 1)
Register Bank 0

38. Timer :
38

39. 39

40. 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.
40

41. 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.
41

42. Interrupt :
42

43. Interrupt Enable Register :
 EA : Global enable/disable.
 ---
: Undefined.
 ET2 :Enable Timer 2 interrupt.
 ES :Enable Serial port interrupt.
 ET1 :Enable Timer 1 interrupt.
 EX1 :Enable External 1 interrupt.
 ET0 : Enable Timer 0 interrupt.
 EX0 : Enable External 0 interrupt.
43

44. References
 “The 8051 Microcontroller and Embedded System” by
Muhammad Ali Mazidi & Janice Gillespie Mazidi.
 “INTEL MCS-51” Wikipedia,
http://en.wikipedia.org/wiki/Intel_MCS-51
• “INTEL 8051” Wikipedia,
http://it.wikipedia.org/wiki/Intel_8051
• “Keil 8051 Microcontroller Development Tools-Keil
uVision4”
www.keil.com/c51/
 “User guide to use Keil uVision4” in Youtube
http://www.youtube.com/watch?v=sdJFLVdApXQ
44