assigment 1 report

8/3/2019 Assigment 1 Report

http://slidepdf.com/reader/full/assigment-1-report 1/20

Abstract

Embedded system might appear less user friendly to most people but the reality is that all the

systems they think to be more user friendly are composed of one or more embedded systems.

Moreover, the use of embedded systems in the design of our daily used devices is becoming

inevitable.

The design and simulation of a serial terminal device which can be control remotely has been

illustrated in this report. Focus has been on the interfacing of peripheral devices such as

keypads, LCD and virtual terminals to a microcontroller.

1



1.0 Introduction

Embedded systems come in handy when a system needs to be cost effective and still delivers

its purpose of design efficiently. Thus embedded systems can be defined as computing

systems with tightly coupled hardware and software integration, which are designed to

perform a specific task [1]. Though it limits the developer’s ability to exploit the system, it

has all the components needed to perform a designated function. Embedded systems can

found in most of our daily used devices such MP3, printers, routers, and even vehicles.

Basically, embedded systems are microcontrollers or microprocessors which are quite

different from the traditional processors which serve general purpose functions. This project

will be focusing on PIC microcontroller and it interface with some peripheral devices. It will

also look expected results when the interfaced circuit is simulated using the MPLAB

software.

2.0 Problem Analysis

2



This project has been aimed to design a serial terminal system to control a remotely operated

4-bit pattern generator. A PIC18F4520 microcontroller will be interfaced with a Liquid

Crystal Display (LCD) and a numeric keypad. Each of the four I/O pins will be

independently controllable to provide steady state high and low or pulse signal with

separately controllable high of low periods within 1ms – 5s. The current state of the device

will be shown by a liquid Cristal Display (LCD) which will also be used as a user interface

during the adjustment of the pattern generator through a numeric keypad. The expected

results when the system is designed using a FreeRTOS running on a PIC18F4520

microcontroller will be discussed.

The serial connection can be used for debugging purposes. But since its function it not very

evident in this project, it will be rarely conversed. Figure 1.0 shows a simplified block

diagram of the device interconnectivity.

Figure 1.0: Block Diagram of Component Interconnections

3.0 Problem Solution

3

MICROCONTROLLER

LCD DISPLAY

SERIAL

CONNECTIO

KEYPAD

I/O



A PIC18F4520 will be used as microcontroller generating the 4-bit pattern; a LM016L will

serve as the LCD to display device status while the KEYPAD-PHONE will be the numeric

keypad for manipulating the pattern generator. The FreeRTOS will be used to write a C code

to implement the system and finally simulation and testing will be done using the MPLAB

IDE and the Proteus VSM.

3.1 Hardware Component Overview

Components needed for this project are:

• Microcontroller - PIC18F4520

• LCD - LM016L

• Numeric keypad – KEYPAD-PHONE

• Virtual terminal - Serial Port

3.1.1 Microcontroller - PIC18F4520

In general, PIC microcontrollers are very common and often used by developers because the

availability of development tools such as compilers, assemblers, debuggers and emulators.

Moreover, it is believed to come from a reliable source - Microchip Technology Corporation.

However, this project will be using a microcontroller from PIC18 family which has RISC

architecture with on-chip program ROM, data RAM, data EEPROM, timers, ADC and

USART and I/O ports.

PIC18F4520 particularly has the following advantages:

•

Economically high computational power (nanoWatt Technology)

• High endurance

• Enhanced flash program memory

• Design enhancement capability

4



Figure 2.0: PIC18F4520 Microcontroller

5



Features PIC18F4520

Operating frequency DC – 40 MHz

Program memory (bytes) 32768

Program Memory(Instructions) 16384

data memory(bytes) 1536

data EEPROM memory(bytes) 256Interupt Sources 20

I/O Ports Ports A,B,C,D,E

Timers 4

Capture/Compare/PWM Modules 1

Enhanced Capture/Compare/PWM Modules 1

Serial communications MSSP, Enhanced USART

Parallel Communications (PSP) Yes

10-bits A/D Module 13 Input Channels

Resets (and delays) POR, BOR, RESET INSTRUCTION, Stack

Underflow (PWRT,OST), MCLR (optional),

WDT

Programmable High/low-voltage detect Yes

Programmable Brown-out reset Yes

Instruction Set 75 Instructions; 83 with Extended Instruction

Set Enabled

Packages 40-Pin PDIP

44-Pin QFN

44-Pin TQFPTable 1.0: PIC18F4520 Features

3.1.2 LCD - LM016L

LCDs are becoming more popular and commonly used as user interface displays in

embedded system design because of its numerous advantages over the traditional LEDs.

These advantages include:

• Unlike LEDs it can display graphics in addition to numbers and characters

• Characters and graphics are easily programmed

• Gets cheaper by the day

• Ability to refresh on its own

6



LM016L comprises of 14 pins as shown in Table 2.0

Pin Symbol I/O Description

1 Vss -- Ground

2 Vcc -- +5 V power supply

3 VEE -- Power supply to

control contrast

4 RS I RS = 0 to select

command register,

RS = 1to select data

register

5 RW I R/W = 0 for write,

R/W = 1 for read

6 E I/O Enable7 DB0 I/O The 8-bit data bus

8 DB1 I/O The 8-bit data bus







Table 2.0: Pin position of the LCD

3.1.3 Numeric keypad – KEYPAD-PHONE

7



Figure 3.0: Internal structure of keypad phone

Just as briefly shown in Figure 3.0, the keypad is organised in 3X4 matrix of rows and

columns which is accessed by the microcontroller through ports. This access always involves

two processes, key detection and key identification, when programming the interfaced

keypad. The processor can implement the key detection process by using either interrupt

method or scanning method as shown in Figure 4.0.

8

No

Start

Ground all rows

Read all columns

Al

keys

ope

n?

Ground next row

Read all

Row

identified?

1



Figure 4.0: a flow chat of the key press detection (Interrupt method)[2]

3.1.4 Serial Port

Serial data communication transfers data using two methods, asynchronous and synchronous,

which is done one bit at a time as opposed to the parallel communication. It can be connected

to interfaces such as Ethernet, firewire, USB etc enabling the device to be operated efficiently

from a remote location.

3.2 Software Components overview

• FreeRTOS - “FreeRTOS is a small footprint, premtive, open source, real time kernel

that has been designed specifically for use on microcontroller”[3]. It is becoming very

popular now with a lot of developers switching to its use because of the following

features: pre-emptive r co-operation, flexible task priority assignment, queues, binary

9

Yes

Yes

Initialise RBIF

Wait for interrupt

RBIF

?

Wait for

debounce

Read all columns

Find which key is

pressed

Get scan code

from table

Return frominterrupt

1



semaphores, counting semaphores, recursive semaphores etc. But unfortunately, it has

been rarely used in this project for reasons explained later in this report.

• Protues Virtual System Modelling (VSM) – this a software that “combines mixed

mode spice circuit simulation, animated components and microprocessor models to

facilitate co- simulation of complete microcontroller based designs”[4]. It has played

a major role in the accomplishment of this project. If you can design a circuit using

this software (which is not very hard), then the physical prototype of your design will

be run through.

• MPLAB Integrated Development Environment (IDE) – “is a free, integrated toolset

for the development of embedded applications employing Microchip PIC and dsPIC

microcontrollers”[5]. This software has been used to write and compile the C program

that runs the LCD.

4.0 Problem Implementations

4.1 LM016L (LCD) Interfacing

10



Figure 5.0: LCD Interfacing

This LCD consists of 14 pins as show in figure 0.0 where the Vcc was used to supply +5V

and the Vss terminal was connected to the ground while the VEE was used to control the

contrast of the LCD. The RS pin was used to allow the sending of commands to the LCD

when it was set to 0 (RS = 0) and also the sending of data to be shown on the LCD when RS

is set to 1 (RS =1). Moreover, the R/W (Read/Write) pin was used to allow the reading of information from the LCD when it set to 1 (R/W = 1) and when set to 0 (R/W = 0) allows the

writing of information to LCD. T o latch information that is currently at the LCD’s data pins,

a high-low pulse was sent to the En pin. The 8-bit data pins of the LCD are basically used to

send information or read the content of the LCD. However, there are two methods of sending

either commands or data to the LCD.

• Implementing a delay before sending the next character

• Using the busy flag to Verify that the LCD is ready for the next character

4.2 Numeric keypad – KEYPAD-PHONE interfacing

11



Figure 6.0: Keypad Interfacing

Two methods can be employed for the key press detection of the keypad:

• Interrupt method- using the PORTB-Change, the rows are connected to the

PORTB.Low and the columns are connected to PORTB.High such that any changes

made to the pins (connected to the column) will cause an interrupt signifying a key press.

• Scanning method- the processor provides 0 to the output latch by grounding all the

rows then reads data from the columns, unless these data are not equal to 1111, a key

has not been pressed. The microcontroller continues to loop this process until a key

press is identified.

4.3 Device implementation

12



Figure 7.0: Device Interfacing

The circuit, as shown in Figure 7.0, was designed using Protues VSM and was supposed to be

simulated using the MPLAB IDE. The MPLAB which act as assembler, linker and simulator

is a PIC microcontroller tool provided for free by Microchip Corporation. The program was

written using a C programming language.

4.3.1 A Pseudocode on how the system program works

Displays a request, “Pls Enter Pin No.”, for the user to select an output channel on the LCD

(line 1)

Check keypad to identify key pressed

Verify that a valid key has been pressed if not keep requesting for a valid user input

Display a request, “Pls enter pulse width”, for the user to enter the pulse period of the signal

Verify that 1ms ≥ input ≤ 5s if not keep requesting for a valid period within the period range

Display the output pin number on line 1 and the pin status on line 2

Return to keypad scan

4.3.2 Additional sub program for enhanced performance

13



If “ * ” key is pressed, decrement the pulse width by 1ms unless it is already 1ms

If “ # “ key is pressed increment the pulse width by 1ms unless it is already 5s

Figure 8.0 shows the flow chart of the system operation

Figure 8.0: System Flow Chart

5.0 Results

When the device is powered (simulated), a user input request (“ Pls Enter Output pin “) is

displayed on the LCD indicating that the device is well interfaced. This is the only output

14

No

LCD display:

channel

Vali

d

entr

y ?

Keypress

LCD display: enter

period

Keypress

1ms ≥ delay

≤ 5s ?

1

LCD display:

enter channel

Return to

scan

keypads

1Start

Yes

No

Yes



produced by device since the programs for other components has not been included. Figure

9.0 shows the simulated device on ISIS.

Figure 9.0 Device in Running Mode

6.0 Discussion of Results

Ideally the status of any of the output pins is to be displayed on the LCD with respect to the

user input through the keypad. But the program to run the numeric keypad and the

microcontroller was unavailable, so only the LCD which had its program well written was

running on the device. Moreover, the fact that the LCD was able to come on and display the

required characters showed that it has been properly connected to the microcontroller.

Besides, the LCD did not display anything initially after interfacing it with microcontroller. I

had to connect a resistor to the RE3 pin of the microcontroller which acts as a reset. There

was also limited time for me to carry out some required research to improve the current

performance of the system.

However, it would have been more challenging and interesting if all the required codes for the device components was available. Though it would take more time and dedication, a more

15



intrinsic understanding of the device operation would have been appreciated. Nevertheless,

was happy to have designed a working embedded system.

7.0 Conclusion

The design and simulation of an embedded system device to provide a serial terminal and

remote control of a 4-bit I/O has been the aim of this project. All the required components

16



was able to be interfaced but only the LCD, which had its code written, was able to run fully

during simulation

On completion of the project, I realised that embedded systems, known for its limited user

interface, should be carefully designed to avoid confusion or misunderstanding to end users.

This project, though basically software has all the required ideas to produce a physical

hardware prototype.

This project can be said to be a fundamental to many embedded system design because of it

structure and application. Its application can be found in weather monitoring devices where

the user does not necessarily be in this location with the device.

References

[1] Qing, L. (2003) Real-Time Concepts for Embedded Systems. New York: Elsevier Science

& Technology.

17



[2] Mazidi, M. (2008) PIC Microcontroller and Embedded Systems Using Assembly and C

PIC18. New Jersey: Pearson Education, Inc.,

[3] Barry, R. Summary Information on FreeRTOS project and the FreeRTOS product family.

[Online] (http://www.freertos.org/). 2010. (Accessed Decenmber 7, 2010).

[4] Labcenter Electronics, The VSM Advantage. [Online] (URL

http://www.labcenter.com/products/vsm_overview.cfm). (Accessed December 5, 2010).

[5] Microchip, MPLAB Integrated Development Environment. [Online] (URL

http://www.microchip.com/stellent/idcplg?

IdcService=SS_GET_PAGE&nodeId=1406&dDocName=en019469&part=SW007002).

2010. (Accessed December 9, 2010).

Appendices

18

http://www.freertos.org/

http://www.labcenter.com/products/vsm_overview.cfm

http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1406&dDocName=en019469&part=SW007002


http://www.freertos.org/

http://www.labcenter.com/products/vsm_overview.cfm





Appendix 1 Bill of Materials

19



Appendix 2: Programming and compilation using MPLAB

Appendix 3: Designed Circuit on Run Mode

20

assigment 1 report

Documents