SA H - site.iugaza.edu.pssite.iugaza.edu.ps/mawad/wp-content/uploads/Lab2_Basic...

Feb. 2014

By

: EN

G. W

AF

AA

AU

DA

H

By

: EN

G. W

AL

EE

D M

OU

SA

2

2 Embedded Systems Lab

Objectives

- To know how to use switches, push buttons, LEDs and 7-segments.

- To know the meaning and implementation of 7-segment multiplexing.

- To be more familiar with mikrobasic and assembly codes.

Switches and Buttons

Switches and buttons are the basic input devices used to supply certain

voltage level for microcontrollers. Button/switch is a mechanical component

which connects or disconnects two points A and B over its contacts. By

function, button/switch contacts can be normally open or normally closed.

Basic I/O


Switches

Mikrobasic

- DIPSW consists of 8 switches that contain on/off choices.

- It has two sides, one is connected to power source and the other is

connected into the PIC.

- Resistor is needed (as will be shown later with button).

- We can get it from Proteus by keyword “dipsw” then choose the

type 8.

Note

Work with switch doesn’t

need specific extra code,

PIC just deal with it as input

bits (0 & 1) across its pins.

1. Write a program that inputs data from port D (by DIPSW) and

sends it to portB.

2. Simulate the circuit using Proteus ISIS program.

Lab Work 1


Assembly

Proteus

Move from file register

to another destination

(wreg here).

<< Two stages >>

Move from file register

to file register directly.

<< One stage >>


Push-Buttons

Buttons can be connected to the microcontroller in one of two ways:

Button with pull down resistor

o When the button is presses it will supply logical one (+5V) to MCU.

o When the button is not pressed the pull down resistor will supply logical

zero(0v) to the MCU.

Button with pull up resistor

o When the button is presses it will supply logical zero(0v) to the MCU.

o When the button is not pressed the pull up resistor will supply logical

one (+5V) to MCU.

- Push button is connected to power and the PIC with its two sides.

- Pull down resistor will be used through the work in order to avoid

Floating case (Not Zero & not 5V): if there is no resistor and the user

doesn’t press the button, this case happened which means no

constant state for the button … it is problem!! , so pull-down

resistor is needed to give ‘0’ state normally.

- We can get it from Proteus by keyword “push” then choose first

choice.


Proteus

The needed time for the user to press the push button is approximately 200

ms, the speed of the PIC’s work is very high, so ‘while true’ loop will be

executed a lot of times through this period (200 ms), which means that

button has been pressed many times, but in fact the user did it just once!!

So delay is needed .. we can use 300 ms for general use

Note

1. Write a Mikrobasic program that toggles a LED when clicking

on a push button.

Lab Work 2


Mikrobasic

How to think …

- We need to check the status of button: using “if” conditional.

If condition then

‘your action

end if

- Condition : porta.2=1 (just one “=”).

- We need to check the 2nd bit of porta “porta.2”.

- Toggle can be made by xor (x xor 1= x’).

- Delay is needed after “if” in order to let the PIC see just one press on

the button.

- If we want to toggle all bits of the port: xor 0xff.


2. If we want to toggle an enterd number (ex: 0x05) and show the

result into leds.

Mikrobasic

Proteus

Assembly


How to think …

- 3 important items we will make in order to build a

corresponding assembly code to mikrobasic code:

1. toggle: comf portd (complement file reg.)

2. loop (in order to make the work continuous)

x your code

goto x (equals ‘while true’, x as a label)

3. delay (to see the states clearly)

Delay details will be shown later at course and lab,

here some important notes are needed to be

understood now.

- The principle of the delay is that we count down

from a previously set number, and when it reaches

zero, we stop counting. The zero value indicates the

end of the delay, and we continue on our way

through the program. The largest number we can

have is 255 or FF h in hex

- ‘delay’ as a label of the function, end with ‘return’.

- .255: “.” means decimal number.

- Movwf 0x30: location in memory to store number.

- Decfsz: decrement file register skip if zero.

- Inner loop (1l) executed inside outer loop (l2); total

= 255*255 times.


Seven Segment Display

Seven-segment displays are commonly used in electronics as a method of

displaying decimal numeric feedback on the internal operations of devices. A seven

segment display, as its name indicates, is composed of seven elements.

Individually on or off, they can be combined to produce simplified representations

of the Hindu-Arabic numerals. The most commonly used is so called 7- segment

display.

It is composed of 8 LEDs- 7 segments are arranged as a rectangle for symbol

displaying and there is an additional segment for decimal point displaying. The

segments of a 7 segment display are referred to by the letters A to G, as follows:


Seven segment display can be divided into 2 types of connection.

One is called common anode of which all the anodes of the LEDs are

connected together, leaving the cathodes open for connection.

The other one is called common cathode of which all the cathodes of the

LEDs are connected together, leaving the anodes open for connection.

Through the lab we will use common cathode 7-segment

Pins to work << VCC

Enable << GND


To view a number (ex: 5H) on 7-segment, just load its 7-seg representation number

to the port

g f e d c b a

5H: 0 1 1 0 1 1 0 1 => 6d

Mikrobasic Assembly

Proteus


Mikrobasic

How to think …

- In order to make work easier, we will build a function that

get the 7-seg representation of number 0-9.

- Function is written before main.

- sub function name (parameter : dim name as type) as

returned type.

- Ends with end sub.

- dealing with many states (0-9) can be easier with select case

(as: switch (case) in JAVA).

- select ends with end select.

1. Write a program that counts form 0-9 and displays the digits

on the 7-seg.


Lab Work 3


Function


Main

Assembly

Nothing is new !!

Just load numbers << make

a delay …

(no use of converting

function)

How to think …

- We will call a function with a number (0-

9), so we need to have variable: counter.

- We can view initial number on the 7-seg.

- Counter value must be incremented with

a delay between each number.

- Counter must be returned to 0 after 9.


7-segment Multiplexing

The simplest way to drive a display is via a display driver. These are available for up

to 4 displays. Alternatively displays can be driven by a microcontroller and if more

than one display is required, the method of driving them is called "multiplexing."

If a single display is to be driven from a microcontroller, 7 lines will be needed plus

one for the decimal point. For each additional display, only one extra line is needed.

To produce a 4, 5 or 6 digit display, all the 7- segment displays are connected in

parallel. The common line (the common-cathode line) is taken out separately and

this line is taken low for a short period of time to turn on the display.

1. Write a program that displays the number ‘27’ on two 7-seg

using multiplexing techniques.


3. Connect the circuit at the hardware kit.

4. Connect the circuit at the hardwatre Kit.

Lab Work 4


Proteus

How to think …

- Instead of reserving two ports to view 2-digits, multiplexing is used.

- One port will be used… but it can’t carry two values at the same time!.

So we will make a trick that: enable just the 1st 7-seg << load first digit

into it << make a short delay << enable just the 2nd 7-seg << load second

digit into it << make a short delay << all in a loop.

- By this way two digits will appear approximately together .. for the

user eyes.

- Load and delay are the same of a previous work, new work will be with

enable.

- Common cathode 7-seg is enabled by GND, here we want to control

enabling. So we connect the enable of both 7-seg to two of PIC pins and

give/don’t them a power as we need.


Mikrobasic Assembly

At hardware work in the lab, the 7-seg at the kit works as the following:

Pins to work << VCC

Enable << VCC

So in order to make the same previous work, you must change porta

values:

- Enable first 7-seg(by 1): 00000001 = 0x01

- Enable second 7-seg(by 1): 00000010 = 0x02

- Enable first 7-seg(by 0):

11111110 = 0xfe

- Enable second 7-seg(by 0):

11111101 = 0xfd


… Good Luck …

1. Write a Mikrobasic code that toggles 3 LEDs when

controlling that with clicking on 3 push buttons.

2. Write an Assembly and Mikrobasic programs that display

‘271’ on three 7-segs using multiplexing techniques.

Bonus

Implement a system that counts from 00 to 99 and

increments every one click on a push button. (Include

code and circuit with short description).

Include all your work for a complete report that contains

codes and simulation work with results.

Homework

- Comment at Mikrobasic: “ ‘ “ - Comment at MPLAB: “ ; “

- To be more familiar with assembly instructions, see:

http://technology.niagarac.on.ca/staff/mboldin/18F_Instruction_Set/

Extra

SA H - site.iugaza.edu.pssite.iugaza.edu.ps/mawad/wp-content/uploads/Lab2_Basic...

Documents

Transcript of SA H - site.iugaza.edu.pssite.iugaza.edu.ps/mawad/wp-content/uploads/Lab2_Basic...