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giáo trình visual basic và pic phần 1

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Lập trình Visual Basic ngày càng được yêu cầu trong các dự án phần mềm hiện nay. Để đáp ứng yêu cầu về học tập các bạn sinh viên, nhất là sinh viên chuyên ngành tin học, Khoa Công Nghệ Thông Tin, chúng tôi đã tiến hành biên soạn các giáo trình, bài giảng chính trong chương trình học.

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  1. Understanding and Using Visual Basic "Micro-News" Micro-Mailing-List Microcontroller applications with the Basic Stamp, PIC, 8051 and various others can often be enhanced with the use of the PC serial port, and a software interface. Designing your own custom interface software for your next microcontroller application isn't as hard as you may think. Using the PC serial port to interface to the outside world, and your next microcontroller application, can provide you with some extremely powerful software/hardware solutions. This series of articles by Jared Hoylman will walk you through a few of the basic concepts, and then move on to the more advanced areas of communicating with your hardware, and having your hardware communicate back to the PC. Introduction: Option Explicit DataTypes Parsing Strings Advanced Parsing Sending Data From The PC to a Microcontroller Receiving Data From The Microcontroller http://www.rentron.com/VisualBasic.htm (1 of 2)5/25/2004 8:47:02 PM
  2. Understanding and Using Visual Basic Copyright © 1999-2001 Reynolds Electronics | Contact Information | Reynolds Electronics 3101 Eastridge Lane Canon City, Co. 81212 Voice: (719) 269-3469 Fax: (719) 276-2853 http://www.rentron.com/VisualBasic.htm (2 of 2)5/25/2004 8:47:02 PM
  3. Using Visual Basic "Micro-News" Micro-Mailing-List Understanding and Using Visual Basic Part 1 By: Jared Hoylman - Being a VB programmer there are many things that I have picked up over the past few years that greatly improved my programs and programming ability. In this series of articles I am going to cover some of the basics of VB programming and some Tips and Tricks to ease you along your way. This series of articles will start with the basic skills needed and work it's way up to the more advanced topics such as sending and receiving data from a Basic Stamp or Microchip PIC..! Option Explicit I am sure many of you have seen the words Option Explicit at the top of some VB code before. Why is it there, and what does it do..? Well, the Option Explicit statement forces you to declare your variables before you use them. Whoop-t-do, right..? Wrong..! These two simple word can save you hours of headaches debugging your programs..! It can also speed up your program considerably if used right..! By placing Option Explicit at the top of every code module before any procedures you can guarantee that you will not misspell any variables. Lets see an example... http://www.rentron.com/intro.htm (1 of 3)5/25/2004 8:47:24 PM
  4. Using Visual Basic Private Sub Command1_Click() Dim sMississippi As String sMississipi = "Hello" '
  5. Using Visual Basic Copyright © 1999-2002 Reynolds Electronics | Contact Information | Reynolds Electronics 3101 Eastridge Lane Canon City, Co. 81212 Voice: (719) 269-3469 Fax: (719) 276-2853 http://www.rentron.com/intro.htm (3 of 3)5/25/2004 8:47:24 PM
  6. Visual Basic Datatypes "Micro-News" Micro-Mailing-List Understanding and Using Visual Basic Part 2 By: Jared Hoylman - Understanding and Optimizing Data Types In Visual Basic 6 there are 11 different data types. These are Boolean, Byte, Currency, Date, Double, Integer, Long, Object, Single, String, and Variant. They each have a specific purpose and using them correctly will increase your programs performance. I am going to cover the data types most frequently used. • Boolean The Boolean data type has only two states, True and False. These types of variables are stored as 16-bit (2 Byte) numbers, and are usually used for flags. For example, lets say that you have a textbox (Text1) and a command button (Command1). You only want Command1 to be Enabled when there is text in Text1. You would do something like this... Private Sub Form_Load() Command1.Enabled = False ' Disables Command1 Text1.Text = vbNullString ' Sets Text1="" End Sub Private Sub Text1_Change() Dim bEnable As Boolean If Text1.Text "" Then bEnable = True Command1.Enabled = bEnable End Sub http://www.rentron.com/datatypes.htm (1 of 4)5/25/2004 8:47:40 PM
  7. Visual Basic Datatypes Run the program and Command1 will only be enabled when there is text typed into Text1. • Byte The Byte data type is an 8-bit variable which can store value from 0 to 255. This data type is very useful for storing binary data. It can also be very useful when sending/receiving byte values to/from a Basic Stamp or PIC. • Double The Double data type is a 64-bit floating point number used when high accuracy is needed. These variables can range from - 1.79769313486232e308 to -4.94065645841247e-324 for negative values and from 4.94065645841247e-324 to 1.79769313486232e308 for positive values. • Integer The Integer data type is a 16-bit number which can range from -32768 to 32767. Integers should be used when you are working with values that can not contain fractional numbers. • Long The Long data type is a 32-bit number which can range from - 2,147,483,648 to 2,147,483,647. Long variables can only contain non- fractional integer values. I myself use Long variables over Integers for increased performance. Most Win32 functions use this data type for this reason. • Single The Single data type is a 32-bit number ranging from -3.402823e38 to - 1.401298e-45 for negative values and from 1.401298e-45 to 3.402823e38 for positive values. When you need fractional numbers within this range, this is the data type to use. • String The String data type is usually used as a variable-length type of variable. A variable-length string can contain up to approximately 2 billion characters. Each character has a value ranging from 0 to 255 based on the ASCII character set. Strings are used when Text is involved. Putting All Of This Technical Stuff To Use Just to show you how to use these data types, here is a small example. Lets say that we have a String containing the text, "This VB stuff is pretty http://www.rentron.com/datatypes.htm (2 of 4)5/25/2004 8:47:40 PM
  8. Visual Basic Datatypes darn cool..!", and we want to convert each letter to it's ASCII equivalent. We will then display each letter along with its ASCII equivalent in a MessageBox one at a time. Private Sub Command1_Click() Dim sText As String Dim lTextLength As Long Dim sChar As String Dim bASCII As Byte Dim x As Long sText = "This VB stuff is pretty darn cool..!" lTextLength = Len(sText) 'Gets # of chars in sText For x = 1 To lTextLength 'Loop through string one char at a time sChar = Mid$(sText, x, 1)'Gets the x'th charcter in sText bASCII = Asc(sChar) 'Gets ASCII value of character MsgBox "The ASCII value of '" & sChar & "' is " & bASCII 'Display results Next x End Sub Now run the code and it will display one character at a time along with it's ASCII value. > Copyright © 1999-2001 Reynolds Electronics | Contact Information | Reynolds Electronics 3101 Eastridge Lane Canon City, Co. 81212 Voice: (719) 269-3469 Fax: (719) 276-2853 http://www.rentron.com/datatypes.htm (3 of 4)5/25/2004 8:47:40 PM
  9. Visual Basic Datatypes http://www.rentron.com/datatypes.htm (4 of 4)5/25/2004 8:47:40 PM
  10. Visual Basic Parsing Strings "Micro-News" Micro-Mailing-List Understanding and Using Visual Basic Part 3 By: Jared Hoylman - Parsing Strings Strings are one of the most widely used data types, and yet parsing strings is one of the most mis-understood concepts to Visual Basic programmers. So I will show you how it is done. • The Len Function The Len function simply returns the number of characters within a string. For example... Dim sText As String Dim lTextLength As Long sText = "Reynolds Electronics" lTextLength = Len(sText) After running this code lTextLength will equal 20, which is the number of characters in the string sText • The InStr Function The InStr function will tell you if a string is within a string and where it starts. For example... http://www.rentron.com/parsingstrings.htm (1 of 5)5/25/2004 8:47:51 PM
  11. Visual Basic Parsing Strings Dim sText As String Dim lElectronics As Long sText = "Reynolds Electronics" lElectronics = InStr(sText, "Electronics") After running this code lElectronics will contain the value 10. If you count over from the beginning of the string you will notice that the word Electronics begins at the tenth letter of sText. You can also use the Instr function just to determine whether a string is present within another string. Dim sText As String Dim lElectronics As Long sText = "Reynolds Electronics" If InStr(sText, "Electronics") Then MsgBox "Found the word 'Electronics'" Else MsgBox "Did not find the word 'Electronics'" End If Run this code and it should tell you that it found the word Electronics. Now try changing sText to something else and run it again to see what happens... • The Left Function The Left function returns a specified number of characters from the left side of a string. For example run the following code and the results should show up in your Debug window. http://www.rentron.com/parsingstrings.htm (2 of 5)5/25/2004 8:47:51 PM
  12. Visual Basic Parsing Strings Dim sText As String Dim sLeft1 As String Dim sLeft5 As String Dim sLeft15 As String sText = "Reynolds Electronics" sLeft1 = Left$(sText, 1) sLeft5 = Left$(sText, 5) sLeft15 = Left$(sText, 15) Debug.Print "The first letter is: " & sLeft1 Debug.Print "The first 5 letters are: " & sLeft5 Debug.Print "The first 15 letters are: " & sLeft15 • The Right Function The Right function returns a specified number of characters from the right side of a string. For example run the following code and the results should show up in your Debug window. Dim sText As String Dim sRight1 As String Dim sRight5 As String Dim sRight15 As String sText = "Reynolds Electronics" sRight1 = Right$(sText, 1) sRight5 = Right$(sText, 5) sRight15 = Right$(sText, 15) Debug.Print "The last letter is: " & sRight1 Debug.Print "The last 5 letters are: " & sRight5 Debug.Print "The last 15 letters are: " & sRight15 • The Mid Function Now the Mid function is a little bit trickier so we are going to take this one a little slower. The Mid function needs three values passed to it, the String to search in, a starting position, and a length. What this function actually does is look in a string, starting at the position you tell it to start at, and retrieve the number of characters that you tell it to. So... http://www.rentron.com/parsingstrings.htm (3 of 5)5/25/2004 8:47:51 PM
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