1. Microcontroller
8051

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

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

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

6. Microprocessors: General-purpose microprocessor 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
Data Bus
CPU
General-Purpose Micro-processor
Serial COM Port
I/O Port
Intel’s x86: 8086,8088,80386,80486, Pentium
Motorola’s 680x0: 68000, 68010, 68020,68030,6040
RAM
ROM
Timer
Address Bus
General-Purpose Microprocessor System

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

8. Microprocessor vs. Microcontroller
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
versatility 多用途的: any number of applications for PC

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
processor 整合到整個系統中, 你只看到此系統的外觀, 應用, 感覺不到有 processor 在其中.
Embedded system 通常只有一項應用, 而 PC 有許多 applications (game, accounting, fax, mail...)
A printer is an example of embedded system since the processor inside it performs one task only.

10. 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
availability of software development tools
assemblers, debuggers, C compilers, emulator, simulator, technical support
wide availability and reliable sources of the microcontrollers.

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

13. Pin Description of the 8051 8051  1 2 3 4 5 6 7 8 9 10 11 12 13 14 1516 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 

14. Vcc provides supply voltage to the chip. The voltage source is +5V.
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. Figure (a). XTAL Connection to 8051
Using a quartz crystal oscillator
We can observe the frequency on the XTAL2 pin. C2
30pF C1
XTAL2
XTAL1
GND 

16. It is an input pin and is active high（normally low）.
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. Figure (b). Power-On RESET Circuit
Vcc +
10 uF 31
EA/VPP X1
30 pF 19
MHz
8.2 K X2 18
30 pF
RST 9 

18. /EA（pin 31）：external access
Pins of 8051（3/4）
/EA（pin 31）：external access
There is no on-chip ROM in 8031 and
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. ALE（pin 30）：address latch enable
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. Ex：P0.0 is the bit 0（LSB）of P0 Ex：P0.7 is the bit 7（MSB）of P0
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).
Program is to read data from P0 and then send data to P1 

21. 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”
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

22. D Latch:

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

24. Writing “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 pin
P1.X
TB2
2. output pin is Vcc
1. write a 1 to the pin 1
output 1
TB1
8051 IC

25. Writing “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 pin
P1.X
TB2
2. output pin is ground
1. write a 0 to the pin
output 0 1
TB1
8051 IC

26. Reading “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
2. MOV A,P1
external pin=High
TB2
write a 1 to the pin MOV P1,#0FFH 1 1
TB1
3. Read pin=1 Read latch=0 Write to latch=1
8051 IC

27. Reading “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
2. MOV A,P1
external pin=Low
TB2
write a 1 to the pin
MOV P1,#0FFH 1
TB1
3. Read pin=1 Read latch=0 Write to latch=1
8051 IC

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

30. Port 0 with Pull-Up Resistors
DS5000
8751
8951
Vcc
10 K
Port 0

31. Port 3 Alternate Functions17 RD
P3.7 16 WR
P3.6 15 T1
P3.5 14 T0
P3.4 13
INT1
P3.3 12
INT0
P3.2 11
TxD
P3.1 10
RxD
P3.0
Pin
Function
P3 Bit 

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

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

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

35. 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

36. Stack 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
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.

37. 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.

38. TMOD Register:

39. 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.

40. TCON Register:

41. Interrupt :

42. 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.