Microcontroller

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

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..

Different aspects of a microprocessor/controller
Hardware :Interface to the real world


Software :order how to deal with inputs

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

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

Timer

Serial COM Port

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

RAM ROM

A single chip I/O Port

Serial Timer COM Port

Microcontroller

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

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

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

Three criteria in Choosing a Microcontroller 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 2. availability of software development tools • assemblers, debuggers, C compilers, emulator, simulator, technical support 3. wide availability and reliable sources of the microcontrollers.

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

Serial Port

TxD RxD

Counter Inputs

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

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) P2.5(A13) P2.4(A12) P2.3(A11) P2.2(A10) P2.1(A9) P2.0(A8)



Pins of 8051（ 8051（1/4） 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）

Figure (a). 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



Pins of 8051（ 8051（2/4） 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 

Figure (b). PowerPower-On RESET Circuit Vcc

+ 10 uF

31 30 pF 11.0592 MHz

19

EA/VPP X1

8.2 K 30 pF

18

X2

9 RST



Pins of 8051（ 8051（3/4） 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.

Pins of 8051（ 8051（4/4） 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..

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).



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

D Latch:

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

P0.x

Read pin

8051 IC

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

8051 IC

output 1

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

8051 IC

output 0

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 8051 IC

P1.X pin

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 8051 IC

P1.X pin

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.

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

P1.x

Read pin

8051 IC

Port 0 with PullPull-Up Resistors Vcc

Port

P0.0 DS5000 P0.1 P0.2 8751 P0.3 P0.4 8951 P0.5 P0.6 P0.7

10 K

0

Port 3 Alternate Functions P3 Bit

Function

Pin

P3.0 P3.1 P3.2 P3.3 P3.4 P3.5 P3.6 P3.7

RxD TxD INT0 INT1 INT 1 T0 T1 WR RD

10 11 12 13 14 15 16 17



RESET Value of Some 8051 Registers:

Register PC ACC B PSW SP DPTR RAM are all zero..

Reset Value 0000 0000 0000 0000 0007 0000



Registers A B R0

DPTR

DPH

DPL

R1 R2

PC

PC

R3 R4 R5 R6 R7 Some 8-bitt Registers of the 8051

Some 8051 16-bit Register

Memory mapping in 8051
ROM memory map in 8051 family 4k 0000H

8k

32k 0000H

0000H

0FFFH DS5000-32 8751 AT89C51

1FFFH 8752 AT89C52

7FFFH

from Atmel Corporation from Dallas Semiconductor


RAM memory space allocation in the 8051 7FH Scratch pad RAM

30H 2FH Bit-Addressable RAM 20H 1FH

Register Bank 3

18H 17H 10H 0FH 08H 07H 00H

Register Bank 2 (Stack) Register Bank 1

Register Bank 0

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.

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

Timer :

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.

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 :

Interrupt Enable Register :


EA : Global enable/disable.


---









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..

: Undefined.