Microcontroller 8051

Contents:Contents:
IntroductionIntroduction
Block Diagram andBlock Diagram and Pin Description of the 8051Pin Description of the 8051
RegistersRegisters
Memory mapping in 8051Memory mapping in 8051
Stack in the 8051Stack in the 8051
I/O Port ProgrammingI/O Port Programming
TimerTimer
InterruptInterrupt

Why do we need to learnWhy do we need to learn
Microprocessors/controllers?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..

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

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

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

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

 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
Embedded System

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

Block DiagramBlock Diagram
CPU
On-chip
RAM
On-chip
ROM for
program
code
4 I/O Ports
Timer 0
Serial
PortOSC
Interrupt
Control
External interrupts
Timer 1
Timer/Counter
Bus
Control
TxD RxDP0 P1 P2 P3
Address/Data
Counter
Inputs

Pin Description of the 8051Pin Description of the 8051
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


Pins of 8051Pins of 8051 （（ 1/41/4 ））
 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 ）

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

Pins of 8051Pins of 8051 （（ 2/42/4 ））
 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

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

Pins of 8051Pins of 8051 （（ 3/43/4 ））
 /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.

Pins of 8051Pins of 8051 （（ 4/44/4 ））
 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..

Pins of I/O PortPins 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).


Hardware Structure of I/O PinHardware 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”
– Write 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

A Pin of Port 1A Pin of Port 1
8051 IC
D Q
Clk Q
Vcc
Load(L1)
Read latch
Read pin
Write to latch
Internal CPU
bus
M1
P1.X
pinP1.X
TB1
TB2
P0.x

Writing “1” to Output Pin P1.XWriting “1” to Output Pin P1.X
D Q
Clk Q
Vcc
Load(L1)
Read latch
Read pin
Write to latch
Internal CPU
bus
M1
P1.X
pinP1.X
8051 IC
2. output pin is
Vcc1. write a 1 to the pin
1
0 output 1
TB1
TB2

Writing “0” to Output Pin P1.XWriting “0” to Output Pin P1.X
D Q
Clk Q
Vcc
Load(L1)
Read latch
Read pin
Write to latch
Internal CPU
bus
M1
P1.X
pinP1.X
8051 IC
2. output pin is
ground1. write a 0 to the pin
0
1 output 0
TB1
TB2

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

Reading “Low” at Input PinReading “Low” at Input Pin
D Q
Clk Q
Vcc
Load(L1)
Read latch
Read pin
Write to latch
Internal CPU bus
M1
P1.X pin
P1.X
8051 IC
2. MOV A,P1
external pin=Low1. write a 1 to the pin
MOV P1,#0FFH
1
0
3. Read pin=1 Read latch=0
Write to latch=1
0
TB1
TB2

Other PinsOther 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.

A Pin of Port 0A Pin of Port 0
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

Port 0 with Pull-Up ResistorsPort 0 with Pull-Up Resistors
P0.0
P0.1
P0.2
P0.3
P0.4
P0.5
P0.6
P0.7
DS5000
8751
8951
Vcc
10 K
Port0

Port 3 Alternate FunctionsPort 3 Alternate Functions
1717RDRDP3.7P3.7
1616WRWRP3.6P3.6
1515T1T1P3.5P3.5
1414T0T0P3.4P3.4
1313INT1INT1P3.3P3.3
1212INT0INT0P3.2P3.2
1111TxDTxDP3.1P3.1
1010RxDRxDP3.0P3.0
PinPinFunctionFunctionP3 BitP3 Bit


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

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

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

 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

Stack in the 8051Stack 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.
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

TMOD RegisterTMOD 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.

TCON Register: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.

Interrupt Enable Register :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..

Microcontroller 8051

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