Embedded Systems,Embedded Systems Project,Winter training,

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• The embedded system is a combination of computer hardware,
software additional electrical & mechanical parts
• A computer is used in such devices primarily as a means to simplify
the system design and to provide flexibility.
• Embedded systems employ the use of a RTOS (Real-Time
Operating System).

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Block Diagram of Embedded System


Microcontroller
• A smaller computer.
• On-chip RAM, ROM, I/O ports...
• Example:- Motorola’s 6811, Intel’s 8051 and PIC 16X

CPU

RAM

ROM

I/O
Port

Serial
Timer COM
Port

Microcontroller

A single chip


The 8051 Microcontroller :
•

The 8051 is the first microcontroller of
the MCS-51 family introduced by
Intel Corporation at the end of the
1970’s.

• The 8051 family characteristics:
○ The 8051 family characteristics:
○ 4K Bytes ROM
○ 128 Bytes RAM
○ two timer/counters (16 bit)
○ A serial port
○ 32 input/output port
○ Interrupt controller

8051 Internal Architecture


IC 8051 Pin Description
Voltage Supply
(+5V)

Ground

Port 0 from
Pin-39 to Pin-32
An 8-bit open drain
bidirectional port.

DUAL
FUNCTION
Used to access both
data and address


Port 1 from
Pin-1 to pin-8
8-bit bidirectional
I/O port with
internal pull-ups



Port 2 from
Pin-21 to pin-28
Used to access
address and I/O


P3.0 : RxD(serial input port)
P3.1 :TxD (serial output port)
P3.2 :INT0 (external interrupt 0)
P3.4 :T0 (timer 0 external input)
P3.5 :T1 (timer 1 external input)
P3.6 :WR (external data memory write strobe)
P3.7 :RD (external data memory read strobe)

Port 3 from
Pin-10 to Pin-17



External memory
reset
Add. Latch
enable

Program Store
Enable
crystal

IC 8051 Daily Applications

Moving message display

7

Digital clock

segment display
Traffic

Light

IC 8051 Addressing Modes
•Immediate addressing modes
ADD A, #23h (Add immediate data to Acc)

•Register addressing modes
ADD A, R2 (Add register to Accumulator)

•Direct addressing modes
ADD A, 40h (Add data at location 40h to Accumulator)

•Register Indirect addressing modes
ADD A,@R2 (Add indirect RAM to Acc)


Interrupts in 8051


An interrupt is an external or internal event that interrupts the microcontroller to
inform it that a device needs its service



The advantage of interrupts is that the microcontroller can serve many devices
(not all at the same time)

Program

Program

Interrupt service
time


Interrupts in 8051
EA

-

ET2

ES

ET1

EX1

Internal Interrupts
EX0
ET0
EX1
ET1
ES
ET2
-EA

Enables or disables external interrupt
Enables or disables timer 0 overflow interrupt
Enables or disables external interrupt 1
Enables or disables timer 1 overflow interrupt
Enables or disables the serial port interrupt
Enables or disables timer 2 overflow or capture interrupt
Not implemented, reserved for future use
Disables all interrupts

External Interrupts
P3.3 :INT1www.technogroovy.com,1)
(external interrupt Cell-

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ET0

EX0

General Purpose
Microprocessor
• CPU for Computers
• No RAM, ROM, I/O on CPU chip itself
• Example--Intel’s x86: 8086,8088,80386,80486, Pentium
CPU
GeneralPurpose
Microprocessor

Data Bus

RAM

Many chips on mother
board
ROM

I/O
Port

Timer

Address Bus
General-Purpose Microprocessor System

Serial
COM
Port

The 8085 Microprocessor :
•
•
•
•
•
•

•

The features of INTEL 8085 are :
It is an 8 bit processor.
It is a single chip N-MOS device with
40 pins.
It has multiplexed address and data
bus.(AD0-AD7).
It works on 5 Volt dc power supply.
The maximum clock frequency is 3
MHz while minimum frequency is
500kHz.
It provides 74 instructions with 5
different addressing modes.


•AD0-AD7: Multiplexed Address and data lines.
•A8-A15: Tri-stated higher order address lines.
•ALE: Address latch enable is an output signal.It goes high when operation is
started by processor .

•S0,S1: These are the status signals used to indicate type of operation.
•RD¯: Read is active low input signal used to read data from I/O device or
memory.

•WR¯: Write is an active low output signal used write data on memory or an
I/O device.


• READY: This an output signal used to check the status of output device.If
it is low, µP will WAIT until it is high.
• TRAP: It is an Edge triggered highest priority , non mask able interrupt.
After TRAP, restart occurs and execution starts from address 0024H.
• RST 5.5,6.5,7.5: These are maskable interrupts and have low priority than
TRAP.
• INTR¯&INTA: INTR is a interrupt request signal after which µP generates
INTA or interrupt acknowledge signal.

•IO/M¯: This is output pin or signal used to indicate whether 8085 is working
in I/O mode(IO/M¯=1) or Memory mode(IO/M¯=0 ).

•HOLD&HLDA: HOLD is an input signal .When µP receives HOLD signal it
completes current machine cycle and stops executing next instruction. In
response to HOLD µP generates HLDA that is HOLD Acknowledge signal.

•RESET IN¯: This is input signal. When RESET IN¯ is low µp restarts and starts
executing from location 0000H.

•SID: Serial input data is input pin used to accept serial 1 bit data .
•X1 & X2 : These are clock input signals and are connected to external LC,or
RC circuit.These are divide by two so if 6 MHz is connected to X1X2, the
operating frequency becomes 3 MHz.

•VCC & VSS: Power supply VCC=+ -5Volt& VSS=-GND reference.


8085 Internal Architecture


Arithmetic and Logical Group
Accumulator:
It is 8 bit general purpose register.
It is connected to ALU. So most of the operations are done in Acc.

Temporary register:
All the arithmetic and logical operations are done in the temporary register
but user can’t access it.

Flag:
It is a group of 5 flip flops used to know status of various operations done.
The Flag Register along with Accumulator is called PSW
or Program Status Word.


Arithmetic and Logical Group
Flag is given by :

S

Z

-

AC

-

P

-

S: Sign flag is set when result of an operation is negative.
Z: Zero flag is set when result of an operation is 0.
Ac: Auxiliary carry flag is set when there is a carry out of lower nibble or
lower four bits of the operation.

CY: Carry flag is set when there is carry generated by an operation.
P: Parity flag is set when result contains even number of 1’s.
Rest are www.technogroovy.com, Celldon’t care flip flops.

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CY

Register Group
Temporary registers (W,Z): These are not available for user. These are loaded only
when there is an operation being performed.

General purpose: There are six general purpose registers in 8085 namely

B,C,D,E,H,L These are used for various data manipulations.
Special purpose : There are two special purpose registers in 8085:
SP : (Stack Pointer) This is a temporary storage memory 16 bit register. Since there
are only 6 general purpose registers, there is a need to reuse them

PC: (Program Counter) It is 16 bit register used to point the location from which the
next instruction is to be fetched.

IC 8085 Addressing modes
Immediate addressing:
Immediate data is transferred to address or register.
Example : MVI A,20H

Register addressing:
Data is transferred from one register to other.
Example : MOV A, C

Indirect addressing:
Data is transferred from address pointed by the data in a register to other
register or vice-versa.
Example: MOV A, M

Implied addressing:
These doesn’t require any operand. The data is specified in Opcode itself.
Example: RAL: Rotate left with carry.

Interrupts in 8085


An interrupt is considered to be an emergency signal that may be serviced. The
Microprocessor may respond to it as soon as possible.

Interrupts can also be classified into:



Maskable Interrupts (Can be delayed or Rejected)
Non-Maskable Interrupts (Can not be delayed or Rejected)

The 8085 has 5 interrupt inputs.

The INTR input : INTR is mask-able using the EI/DI instruction pair.
RST 5.5, RST 6.5, RST 7.5 : They are all mask-able.
TRAP : is the only non-mask-able interrupt in the 8085

Interrupts in 8085
The 8085 recognizes 8 RESTART instructions: RST0 - RST7 . Each of these would send
the execution to a predetermined hard-wired memory location:
Restart Instruction

Equivalent to

RST0

CALL 0000H

RST1

CALL 0008H

RST2

CALL 0010H

RST3

CALL 0018H

RST4

CALL 0020H

RST5

CALL 0028H

RST6

CALL 0030H

RST7
CALL 0038H

Timing and State Diagram
•

•

The µP operates with reference to clock signal. The rise and fall of the pulse of the
clock gives one clock cycle.
Each clock cycle is called a T state and a collection of several T states gives a
machine cycle.
Important machine cycles are :

1.
2.
3.
4.
5.

Op-code fetch.
Memory read.
Memory write.
I/Op-read.
I/O write.

•


Timing and State Diagram
Op-code fetch cycle :


Seven Segment Display
Seven segments are electronic
components that can be used to
displaying alphanumeric characters, 7
LED are used (as shown in figure) and is
designed from a dot-point with the size.

pin configuration of seven segment


7 pins of the microcontroller are used to shape the
character of your LED display

Port Relations Microcontroller with pin
7 Segment



Table 1. Configuring the Character 7 Segment Data

8051
Microcontroller
Design Softwares


Software’s
Used

Keil µVision

Top View
Simulator


Express
PCB

Keil µVision IDE
 The µVision IDE from Keil
combines project management,
make facilities, source code
editing, program debugging, and
complete simulation in one
powerful environment. The
µVision development platform is
easy-to-use and helping you
quickly create embedded
programs that work. The µVision
editor and debugger are
integrated in a single application
that provides a seamless
embedded project development
environment.

Top View Simulator
• Topview Simulator gives an
excellent simulation environment
for MCS 51 Microcontroller.

A beginner can learn about 8051
based embedded solutions
without any hardware. An
experienced designer, you may
find most of the required facilities
built in the simulator that
enabling you to complete your
next project without waiting for
the target hardware.


Top View Simulator
A Top View
Simulator
Program


Express PCB
Express PCB allows you to design
schematics and PCB's. It is ideal
for those that are looking to
design anywhere from a two to
four layer circuit board.
A drop and drag design allows
users to pick the components of
the circuit board and drop it
onto the circuit board in the
software program. The designer
can then place various pins in the
circuit board to show where
things need to be connected.
It also has the ability of the
program to show the designer
where there are flaws in their
design.


Express PCB
This way we can include resistors

This way we can include different
kind of IC’s


DC Motor interfacing with
Microcontrollers
DC motors are always preffered over stepper motors.

There are many things which we can do with our DC motor when interfaced
with microcontroller.
For example:
we can control the speed of motor,
we can control the direction of rotation,
we can also do encoding of the rotation made by DC motor i.e. keeping track of
how many turns are made by our motors etc.
Usually H-bridge is preffered way of interfacing a DC motor.
L293D is most used H-Bridge driver IC.

Working of H-Bridge
The name "H-Bridge" is derived from the actual shape of the switching circuit which
control the motion of the motor. It is also known as "Full Bridge". Basically there
are four switching elements in the H-Bridge as shown


Truth Table For H-Bridge
Truth Table
High Left

High Right

Low Left

Low Right

Description

On

Off

Off

On

Motor runs
clockwise

Off

Motor runs
anticlockwise

Off

Motor stops
or
decelerates

On

Motor stops
or
decelerates

Off

On

Off

On

On

Off

On

Off

On


Stepper Motor
Of all motors, step motor is the easiest to control. It's
handling simplicity is really hard to deny - all there
is to do is to bring the sequence of rectangle
impulses to one input of step controller and
direction information to another input. Direction
information is very simple and comes down to
"left" for logical one on that pin and "right" for
logical zero.
Motor control is also very simple - every impulse
makes the motor operating for one step and if
there is no impulse the motor won't start. Pause
between impulses can be shorter or longer and it
defines revolution rate. This rate cannot be infinite
because the motor won't be able to "catch up"
with all the impulses (documentation on specific
motor should contain such information)..

Interfacing of Stepper motor with
8051


Clock-wise Rotation of the Coils
Truth table
1

2

3

4

1

0

0

0

0

1

0

0

0

0

1

0

0

0

0

1


Techogroov
y Systems
India Pvt Ltd
, www.technogroovy.com,
Cell- +91-7500347448 , +917533940322
Mail :
technogroovy@gmail.com

Embedded Systems,Embedded Systems Project,Winter training,

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