hi, i am trying to design chip 8 emulator on visual basic, i have found source code of it but the problem is i am not getting the idea how the code works, i understand some part of it.. please help me.. here is the full source code..

Dim ram(8192) As Byte
Dim stack(256) As Integer
Dim v(256), keydef(16) As Byte
Dim pc, Index, key_choice As Integer
Dim opcode1, opcode2, opcode3, opcode4, sp, key_up, key_down, delaytimer, soundtimer, x, y, i, j, k, c1, c2, c3 As Byte
Dim dbg, Pause, ExtendedScreen As Boolean
Private Declare Function Beep Lib "kernel32" (ByVal dwFreq As Long, ByVal dwDuration As Long) As Long

Private Sub About_Click()
    msg = "VB Chip8 - The first Visual Basic implementation" + vbCrLf
    msg = msg + "of a Chip8 Virtual Machine." + vbCrLf
    msg = msg + "Thanks to unknown autor of original C source code." + vbCrLf
    msg = msg + "This release is beta and won't run many games, yet." + vbCrLf
    msg = msg + "Made by VMA in 2004. This is freeware!" + vbCrLf
    MsgBox msg, vbOKOnly, "About VB Chip-8"
End Sub

//it indicates to debug or not
Private Sub Check1_Click()
    If Check1.Value = 1 Then
        Check1.Value = 1
    Else
        dbg = False
    End If
End Sub


Private Sub Command1_Click(Index As Integer)
    key_choice = 0
    Label1.Caption = "Waiting for key..."
    While key_choice = 0
        DoEvents
    Wend
    keydef(Index + 1) = key_choice
    Command1(Index).Caption = Chr(key_choice)
    Label1.Caption = ""
End Sub

Private Sub Exit_Click()
    End
End Sub

Private Sub Form_KeyDown(KeyCode As Integer, Shift As Integer)
    For a = 1 To 16
        If KeyCode = keydef(a) Then key_down = a
    Next a
    key_choice = KeyCode
End Sub

Private Sub Form_KeyUp(KeyCode As Integer, Shift As Integer)
    key_down = 0
End Sub

// I dont Know what is here happening????????
Private Sub Form_Load()
    keydef(1) = 103
    keydef(2) = 104
    keydef(3) = 105
    keydef(4) = 100
    keydef(5) = 101
    keydef(6) = 102
    keydef(7) = 97
    keydef(8) = 98
    keydef(9) = 99
    keydef(10) = 96
    keydef(11) = 111
    keydef(12) = 106
    keydef(13) = 107
    keydef(14) = 13
    keydef(15) = 103
    keydef(16) = 110
    c1 = 0
    c2 = 200
    c3 = 255
    KeyPreview = True
    Randomize
    Timer1.Enabled = True
    Check1.Value = 1
End Sub

Private Sub Form_Unload(Cancel As Integer)
    End
End Sub

//this punction open the dialouge box to load the ROM file
Private Sub OpenROM_Click()
    Dim b As Byte
    CommonDialog1.ShowOpen
    nome = CommonDialog1.FileName
    If nome <> "" Then
        Open nome For Binary As #1
        While EOF(1) = False
            a = a + 1
            Get #1, a, b
            ram(&H200 - 1 + a) = b
        Wend
        Close #1
    End If
    Reset_Click
End Sub

Private Sub pausex_Click()
    If Pause = True Then
        Pause = False
    Else
        Pause = True
    End If
End Sub

// I dont Know what is here happening????????
Private Sub Reset_Click()
    Picture1.Cls
    pc = &H200
    ram(&H1000) = 96
    ram(&H1001) = 144
    ram(&H1002) = 144
    ram(&H1003) = 144
    ram(&H1004) = 96
    ram(&H1005) = 96
    ram(&H1006) = 224
    ram(&H1007) = 96
    ram(&H1008) = 96
    ram(&H1009) = 240
    ram(&H100A) = 96
    ram(&H100B) = 144
    ram(&H100C) = 32
    ram(&H100D) = 64
    ram(&H100E) = 240
    ram(&H100F) = 224
    ram(&H1010) = 16
    ram(&H1011) = 96
    ram(&H1012) = 16
    ram(&H1013) = 224
    ram(&H1014) = 160
    ram(&H1015) = 160
    ram(&H1016) = 240
    ram(&H1017) = 32
    ram(&H1018) = 32
    ram(&H1019) = 240
    ram(&H101A) = 128
    ram(&H101B) = 240
    ram(&H101C) = 16
    ram(&H101D) = 240
    ram(&H101E) = 240
    ram(&H101F) = 128
    ram(&H1020) = 240
    ram(&H1021) = 144
    ram(&H1022) = 240
    ram(&H1023) = 240
    ram(&H1024) = 16
    ram(&H1025) = 32
    ram(&H1026) = 64
    ram(&H1027) = 128
    ram(&H1028) = 96
    ram(&H1029) = 144
    ram(&H102A) = 96
    ram(&H102B) = 144
    ram(&H102C) = 96
    ram(&H102D) = 240
    ram(&H102E) = 144
    ram(&H102F) = 240
    ram(&H1030) = 16
    ram(&H1031) = 240
    ram(&H1032) = 96
    ram(&H1033) = 144
    ram(&H1034) = 240
    ram(&H1035) = 144
    ram(&H1036) = 144
    ram(&H1037) = 224
    ram(&H1038) = 144
    ram(&H1039) = 224
    ram(&H103A) = 144
    ram(&H103B) = 224
    ram(&H103C) = 112
    ram(&H103D) = 128
    ram(&H103E) = 128
    ram(&H103F) = 128
    ram(&H1040) = 112
    ram(&H1041) = 224
    ram(&H1042) = 144
    ram(&H1043) = 144
    ram(&H1044) = 144
    ram(&H1045) = 224
    ram(&H1046) = 240
    ram(&H1047) = 128
    ram(&H1048) = 224
    ram(&H1049) = 128
    ram(&H104A) = 240
    ram(&H104B) = 240
    ram(&H104C) = 128
    ram(&H104D) = 224
    ram(&H104E) = 128
    ram(&H104F) = 128
    ExtendedScreen = False
    start_cpu
End Sub

Private Sub timer1_Timer()
    If delaytimer > 0 Then delaytimer = delaytimer - 1
    If soundtimer > 0 Then
        Beep 500, soundtimer * 5
        soundtimer = 0
    End If
End Sub

Sub start_cpu()
10:
    If delaytimer > 1 Then delaytimer = delaytimer - 1
    If Pause = False Then
        Interpret
    End If
    For a = 1 To HScroll1.Value
        DoEvents
    Next a
    GoTo 10
End Sub

// I dont Know what is here happening????????
Sub getopcode()
    opcode1 = (ram(pc) And &HF0) / 16
    opcode2 = ram(pc) And &HF
    opcode3 = (ram(pc + 1) And &HF0) / 16
    opcode4 = ram(pc + 1) And &HF
    pc = pc + 2
End Sub

// I dont Know what is here happening???????? and this is the most important part which i have to understand pleasehelp me in this thread to understand all this
Sub Interpret()
    getopcode
    If Check1.Value = 1 Then Text1.Text = Text1.Text + Hex(pc - 2) + ": " + Hex(opcode1) + " " + Hex(opcode2) + " " + Hex(opcode3) + " " + Hex(opcode4) + " -> "
    Select Case opcode1
        Case &H0
            Select Case (opcode3)
                Case &HC
                    If Check1.Value = 1 Then Text1.Text = Text1.Text + "ScrollDown"
                    ScrollDown
                Case &HE
                    Select Case (opcode4)
                        Case &H0:
                            If Check1.Value = 1 Then Text1.Text = Text1.Text + "ClearScreen"
                            ClearScreen
                        Case &HE:
                            If Check1.Value = 1 Then Text1.Text = Text1.Text + "ReturnFromSub"
                            ReturnFromSub
                    End Select
                Case &HF
                    Select Case (opcode4)
                        Case &HB
                            If Check1.Value = 1 Then Text1.Text = Text1.Text + "ScrollRight"
                            ScrollRight
                        Case &HC
                            If Check1.Value = 1 Then Text1.Text = Text1.Text + "ScrollLeft"
                            ScrollLeft
                        Case &HE
                            If Check1.Value = 1 Then Text1.Text = Text1.Text + "DisableExtendedScreen"
                            DisableExtendedScreen
                        Case &HF
                            If Check1.Value = 1 Then Text1.Text = Text1.Text + "EnableExtendedScreen"
                            EnableExtendedScreen
                    End Select
            End Select
        Case &H1
            If Check1.Value = 1 Then Text1.Text = Text1.Text + "JumpToAddress"
            JumpToAddress
        Case &H2
            If Check1.Value = 1 Then Text1.Text = Text1.Text + "JumpToSub"
            JumpToSub
        Case &H3
            If Check1.Value = 1 Then Text1.Text = Text1.Text + "SkipIfRegEqual"
            SkipIfRegEqual
        Case &H4:
            If Check1.Value = 1 Then Text1.Text = Text1.Text + "SkipIfRegNotEqual"
            SkipIfRegNotEqual
        Case &H5
            If Check1.Value = 1 Then Text1.Text = Text1.Text + "SkipIfRegEqualReg"
            SkipIfRegEqualReg
        Case &H6
            If Check1.Value = 1 Then Text1.Text = Text1.Text + "LoadRegWithConstant"
            LoadRegWithConstant
        Case &H7
            If Check1.Value = 1 Then Text1.Text = Text1.Text + "AddConstantToReg"
            AddConstantToReg
        Case &H8
            Select Case (opcode4)
                Case &H0
                    If Check1.Value = 1 Then Text1.Text = Text1.Text + "LoadRegWithReg"
                    LoadRegWithReg
                Case &H1
                    If Check1.Value = 1 Then Text1.Text = Text1.Text + "OrRegWIthReg"
                    OrRegWithReg
                Case &H2
                    If Check1.Value = 1 Then Text1.Text = Text1.Text + "AndRegWithReg"
                    AndRegWithReg
                Case &H3
                    If Check1.Value = 1 Then Text1.Text = Text1.Text + "XorRegWithReg"
                    XorRegWithReg
                Case &H4
                    If Check1.Value = 1 Then Text1.Text = Text1.Text + "AddRegToReg"
                    AddRegToReg
                Case &H5
                    If Check1.Value = 1 Then Text1.Text = Text1.Text + "SubRegFromReg"
                    SubRegFromReg
                Case &H6
                    If Check1.Value = 1 Then Text1.Text = Text1.Text + "ShiftRegRight"
                    ShiftRegRight
                Case &H7
                    If Check1.Value = 1 Then Text1.Text = Text1.Text + "RSubRegFromReg"
                    RSubRegFromReg
                Case &HE
                    If Check1.Value = 1 Then Text1.Text = Text1.Text + "ShiftRegLeft"
                    ShiftRegLeft
            End Select
        Case &H9
            If Check1.Value = 1 Then Text1.Text = Text1.Text + "SkipIfRegNotEqualReg"
            SkipIfRegNotEqualReg
        Case &HA
            If Check1.Value = 1 Then Text1.Text = Text1.Text + "LoadIndexWithConstant"
            LoadIndexWithConstant
        Case &HB
            If Check1.Value = 1 Then Text1.Text = Text1.Text + "JumpToAddressPlusReg0"
            JumpToAddressPlusReg0
        Case &HC
            If Check1.Value = 1 Then Text1.Text = Text1.Text + "CreateRandomNumber"
            CreateRandomNumber
        Case &HD
            If Check1.Value = 1 Then Text1.Text = Text1.Text + "DrawSprite"
            DrawSprite
        Case &HE
            Select Case (opcode3)
                Case &H9
                    If Check1.Value = 1 Then Text1.Text = Text1.Text + "SkipIfKeyPressed"
                    SkipIfKeyPressed
                Case &HA
                    If Check1.Value = 1 Then Text1.Text = Text1.Text + "SkipIfKeyNotPressed"
                    SkipIfKeyNotPressed
            End Select
        Case &HF
            Select Case (opcode3)
                Case &H0
                    Select Case (opcode4)
                        Case &H7
                            If Check1.Value = 1 Then Text1.Text = Text1.Text + "GetDelayTimerIntoReg"
                            GetDelayTimerIntoReg
                        Case &HA
                            If Check1.Value = 1 Then Text1.Text = Text1.Text + "WaitForKeyPress"
                            WaitForKeyPress
                    End Select
                Case &H1
                    Select Case (opcode4)
                        Case &H5
                            If Check1.Value = 1 Then Text1.Text = Text1.Text + "SetDelayTimer"
                            SetDelayTimer
                        Case &H8
                            If Check1.Value = 1 Then Text1.Text = Text1.Text + "SetSoundTimer"
                            SetSoundTimer
                        Case &HE
                            If Check1.Value = 1 Then Text1.Text = Text1.Text + "AddRegToIndex"
                            AddRegToIndex
                    End Select
                Case &H2
                    If Check1.Value = 1 Then Text1.Text = Text1.Text + "PointIndexToFont"
                    PointIndexToFont
                Case &H3
                    If Check1.Value = 1 Then Text1.Text = Text1.Text + "StoreBCD"
                    StoreBCD
                Case &H5
                    If Check1.Value = 1 Then Text1.Text = Text1.Text + "StoreRegsAtIndex"
                    StoreRegsAtIndex
                Case &H6
                    If Check1.Value = 1 Then Text1.Text = Text1.Text + "LoadRegsFromIndex"
                    LoadRegsFromIndex
            End Select
    End Select
    If Check1.Value = 1 Then
        Text1.Text = Text1.Text + vbCrLf
        Text1.SelLength = Len(Text1.Text)
    End If
End Sub
Sub ScrollDown()
    For z = 0 To opcode4
        Picture2.PaintPicture Picture1.Image, 0, 2, , , 0, 0
        Picture2.Line (0, 0)-(256, 1), RGB(0, 0, 0), BF
        Picture1.PaintPicture Picture2.Image, 0, 0
    Next z
End Sub

Sub ScrollRight()
    For z = 0 To 3
        Picture2.PaintPicture Picture1.Image, 2, 0, , , 0, 0
        Picture2.Line (0, 0)-(1, 128), RGB(0, 0, 0), BF
        Picture1.PaintPicture Picture2.Image, 0, 0
    Next z
End Sub

Sub ScrollLeft()
    For z = 0 To 3
        Picture2.PaintPicture Picture1.Image, 0, 0, , , 2, 0
        Picture2.Line (255, 0)-(256, 128), RGB(0, 0, 0), BF
        Picture1.PaintPicture Picture2.Image, 0, 0
    Next z
End Sub

Sub DisableExtendedScreen()
    ExtendedScreen = False
End Sub

Sub EnableExtendedScreen()
    ExtendedScreen = True
End Sub

Sub ClearScreen()
    DoEvents
    Form1.Picture1.Cls
End Sub

Sub ReturnFromSub()
    DoEvents
    sp = sp - 1
    pc = stack(sp)
End Sub

Sub JumpToAddress()
    DoEvents
    opcode2 = opcode2 * 256
    opcode3 = opcode3 * 16
    pc = opcode2 + opcode3 + opcode4
End Sub

Sub JumpToSub()
    DoEvents
    stack(sp) = pc
    sp = sp + 1
    opcode2 = opcode2 * 256
    opcode3 = opcode3 * 16
    pc = opcode2 + opcode3 + opcode4
End Sub

Sub SkipIfRegEqual()
    DoEvents
    opcode3 = opcode3 * 16
    If v(opcode2) = (opcode3 + opcode4) Then pc = pc + 2
End Sub

Sub SkipIfRegNotEqual()
    DoEvents
    opcode3 = opcode3 * 16
    If v(opcode2) <> (opcode3 + opcode4) Then pc = pc + 2
End Sub

Sub SkipIfRegEqualReg()
    DoEvents
    If v(opcode2) = v(opcode3) Then pc = pc + 2
End Sub

Sub SkipIfRegNotEqualReg()
    DoEvents
    If v(opcode2) <> v(opcode3) Then pc = pc + 2
End Sub

Sub LoadRegWithConstant()
    DoEvents
    opcode3 = opcode3 * 16
    v(opcode2) = (opcode3 + opcode4)
End Sub

Sub AddConstantToReg()
    DoEvents
    opcode3 = opcode3 * 16
    x = v(opcode2) + (opcode3 + opcode4)
    If x > 255 Then x = x - 256
    v(opcode2) = x
End Sub

Sub LoadRegWithReg()
    DoEvents
    v(opcode2) = v(opcode3)
End Sub

Sub OrRegWithReg()
    DoEvents
    v(opcode2) = v(opcode2) Or v(opcode3)
End Sub

Sub AndRegWithReg()
    DoEvents
    v(opcode2) = v(opcode2) And v(opcode3)
End Sub

Sub XorRegWithReg()
    DoEvents
    v(opcode2) = v(opcode2) Xor v(opcode3)
End Sub

Sub AddRegToReg()
    DoEvents
    Dim x As Integer
    If v(opcode2) And v(opcode3) Then
        v(&HF) = 1
    Else
        v(&HF) = 0
    End If
    x = v(opcode2)
    x = x + v(opcode3)
    If x > 255 Then x = x - 256
    v(opcode2) = x
End Sub

Sub SubRegFromReg()
    DoEvents
    Dim x As Single
    If v(opcode2) >= v(opcode3) Then
        v(&HF) = 1
    Else
        v(&HF) = 0
    End If
    x = v(opcode2)
    x = x - v(opcode3)
    If x < 0 Then x = x + 256
    v(opcode2) = x
End Sub

Sub ShiftRegRight()
    DoEvents
    If v(opcode2) And 1 Then
        v(&HF) = 1
    Else
        v(&HF) = 0
    End If
    v(opcode2) = v(opcode2) / 2
End Sub

Sub RSubRegFromReg()
    DoEvents
    Dim x As Single
    If v(opcode2) >= v(opcode3) Then
        v(&HF) = 1
    Else
        v(&HF) = 0
    End If
    x = v(opcode3)
    x = x - v(opcode2)
    If x < 0 Then x = x + 256
    v(opcode2) = x
End Sub

Sub ShiftRegLeft()
    DoEvents
    If v(opcode2) And 128 Then
        v(&HF) = 1
    Else
        v(&HF) = 0
    End If
    x = v(opcode2) * 2
    If x > 255 Then x = x - 256
    v(opcode2) = x
End Sub

Sub LoadIndexWithConstant()
    DoEvents
    opcode2 = opcode2 * 256
    opcode3 = opcode3 * 16
    Index = opcode2 + opcode3 + opcode4
End Sub

Sub JumpToAddressPlusReg0()
    DoEvents
    opcode2 = opcode2 * 256
    opcode3 = opcode3 * 16
    pc = v(0) + opcode2 + opcode3 + opcode4
End Sub

Sub CreateRandomNumber()
    DoEvents
    opcode3 = opcode3 * 16
    v(opcode2) = Int(Rnd * 256) And (opcode3 + opcode4)
End Sub

Sub DrawSprite()
    v(&HF) = 0
    If ExtendedScreen = False Then
    x = v(opcode2) * 4
    y = v(opcode3) * 4
    For j = 0 To opcode4 - 1
        datax = ram(Index + j)
        i = 0
        If datax >= 128 Then
            DrawScreen
            datax = datax - 128
        End If
        i = i + 1
        If datax >= 64 Then
            DrawScreen
            datax = datax - 64
        End If
        i = i + 1
        If datax >= 32 Then
            DrawScreen
            datax = datax - 32
        End If
        i = i + 1
        If datax >= 16 Then
            DrawScreen
            datax = datax - 16
        End If
        i = i + 1
        If datax >= 8 Then
            DrawScreen
            datax = datax - 8
        End If
        i = i + 1
        If datax >= 4 Then
            DrawScreen
            datax = datax - 4
        End If
        i = i + 1
        If datax >= 2 Then
            DrawScreen
            datax = datax - 2
        End If
        i = i + 1
        If datax >= 1 Then
            DrawScreen
            datax = datax - 1
        End If
    Next j
Else
    If opcode4 = 0 Then
        x = v(opcode2) * 2
        y = v(opcode3) * 2
        For k = 0 To 1
            For j = 0 To 15
                i = 0
                datax = ram(Index + j * 2 + k)
                If datax >= 128 Then
                    DrawSChipSprite
                    datax = datax - 128
                End If
                i = i + 1
                If datax >= 64 Then
                    DrawSChipSprite
                    datax = datax - 64
                End If
                i = i + 1
                If datax >= 32 Then
                    DrawSChipSprite
                    datax = datax - 32
                End If
                i = i + 1
                If datax >= 16 Then
                    DrawSChipSprite
                    datax = datax - 16
                End If
                i = i + 1
                If datax >= 8 Then
                    DrawSChipSprite
                    datax = datax - 8
                End If
                i = i + 1
                If datax >= 4 Then
                    DrawSChipSprite
                    datax = datax - 4
                End If
                i = i + 1
                If datax >= 2 Then
                    DrawSChipSprite
                    datax = datax - 2
                End If
                i = i + 1
                If datax >= 1 Then
                    DrawSChipSprite
                    datax = datax - 1
                End If
                i = i + 1
            Next j
        Next k
    Else
        x = v(opcode2) * 2
        y = v(opcode3) * 2
        For j = 0 To opcode4 - 1
            i = 0
            datax = ram(Index + j)
            If datax >= 128 Then
                DrawScreen_SChip
                datax = datax - 128
            End If
            i = i + 1
            If datax >= 64 Then
                DrawScreen_SChip
                datax = datax - 64
            End If
            i = i + 1
            If datax >= 32 Then
                DrawScreen_SChip
                datax = datax - 32
            End If
            i = i + 1
            If datax >= 16 Then
                DrawScreen_SChip
                datax = datax - 16
            End If
            i = i + 1
            If datax >= 8 Then
                DrawScreen_SChip
                datax = datax - 8
            End If
            i = i + 1
            If datax >= 4 Then
                DrawScreen_SChip
                datax = datax - 4
            End If
            i = i + 1
            If datax >= 2 Then
                DrawScreen_SChip
                datax = datax - 2
            End If
            i = i + 1
            If datax >= 1 Then
                DrawScreen_SChip
                datax = datax - 1
            End If
            i = i + 1
        Next j
    End If
End If
End Sub

Sub DrawScreen()
        If Picture1.Point(1 + x + (i * 4), y + (j * 4)) = RGB(c1, c2, c3) Then
            v(&HF) = 1
            Picture1.Line (1 + x + (i * 4), y + (j * 4))-(1 + x + (i * 4) + 3, y + (j * 4) + 3), RGB(0, 0, 0), BF
        Else
            Picture1.Line (1 + x + (i * 4), y + (j * 4))-(1 + x + (i * 4) + 3, y + (j * 4) + 3), RGB(c1, c2, c3), BF
        End If
End Sub

Sub DrawScreen_SChip()
        If Picture1.Point(1 + x + (i * 2), y + (j * 2)) = RGB(c1, c2, c3) Then
            v(&HF) = 1
            Picture1.Line (1 + x + (i * 2), y + (j * 2))-(1 + x + (i * 2) + 1, y + (j * 2) + 1), RGB(0, 0, 0), BF
        Else
            Picture1.Line (1 + x + (i * 2), y + (j * 2))-(1 + x + (i * 2) + 1, y + (j * 2) + 1), RGB(c1, c2, c3), BF
        End If
End Sub

Sub DrawSChipSprite()
        If Picture1.Point(1 + x + k * 16 + (i * 2), y + (j * 2)) = RGB(c1, c2, c3) Then
            v(&HF) = 1
            Picture1.Line (1 + x + k * 16 + (i * 2), y + (j * 2))-(1 + x + k * 16 + (i * 2) + 1, y + (j * 2) + 1), RGB(0, 0, 0), BF
        Else
            Picture1.Line (1 + x + k * 16 + (i * 2), y + (j * 2))-(1 + x + k * 16 + (i * 2) + 1, y + (j * 2) + 1), RGB(c1, c2, c3), BF
        End If
End Sub

Sub SkipIfKeyPressed()
    DoEvents
    If key_down = v(opcode2) Then pc = pc + 2
End Sub

Sub SkipIfKeyNotPressed()
    DoEvents
    If key_down <> v(opcode2) Then pc = pc + 2
End Sub

Sub WaitForKeyPress()
    DoEvents
    key_down = 0
    Label1.Caption = "Waiting for key..."
    While key_down = 0
        DoEvents
    Wend
    v(opcode2) = key_down
    Label1.Caption = ""
End Sub

Sub SetDelayTimer()
    DoEvents
    delaytimer = v(opcode2)
End Sub

Sub GetDelayTimerIntoReg()
    DoEvents
    v(opcode2) = delaytimer
End Sub

Sub SetSoundTimer()
    DoEvents
    soundtimer = v(opcode2)
End Sub

Sub AddRegToIndex()
    DoEvents
    Index = Index + v(opcode2)
End Sub

Sub PointIndexToFont()
    DoEvents
    Index = &H1000 + (v(opcode2) * &H5)
End Sub

Sub StoreBCD()
    DoEvents
    num = v(opcode2)
    For i = 3 To 1 Step -1
        ram(Index + (i - 1)) = num Mod 10
        num = num / 10
    Next i
End Sub

Sub StoreRegsAtIndex()
    DoEvents
    For i = 0 To opcode2
         ram(Index + i) = v(i)
    Next i
End Sub

Sub LoadRegsFromIndex()
    DoEvents
    For i = 0 To opcode2
        v(i) = ram(Index + i)
    Next i
End Sub

i want to understand three main function..
1. interupt()
2. getopcode()
3. Reset_Click()

Firstly, good luck. I am not sure why you want to get involved in something this old, but I suppose it was your decision.

The code is based on old games covering 8 and 16 bit. VERY old.

To learn more about Chip 8, see the following -
http://users.skynet.be/drealmer/chip8/
OR the tutorial on chip8
http://www.pdc.kth.se/~lfo/chip8/CHIP8.htm

For the following,

// I dont Know what is here happening????????Private Sub Form_Load() keydef(1) = 103 keydef(2) = 104 keydef(3) = 105

again very old way of assigning keycodes to certain keyboard strokes - see http://db.apache.org/torque/releases/torque-3.3/village/jcoverage/com/workingdogs/village/KeyDef.html, http://www.lonely-star.org/lge/reference/KeyDef_8h-source.html

// I dont Know what is here happening????????Private Sub Reset_Click() Picture1.Cls pc = &H200 ram(&H1000) = 96 ram(&H1001) = 144

I think what is happening here is the picture is released and your RAM (random access memory) is released and refreshed for optimum use. Again very old. The bit I found when searching for ram(&H1000)=96 ALL showed posts pre 1997 and referred to systems pre 1996.

The last part, the important part for you -

It basically covers gaming options such as scrolling a large picture (background) over the screen from left to right, up or down etc, depending upon the choice made as in keydef. It also "ups" the cpu or ram depending on the selections made. I did not go into detail here, but I hope you can solve most of this. When you are stuck on a particular piece of code, copy it and search google and see what comes up. I have done this with most of your queries and found some answers for you as above.

It will however take some time to write a "tutorial" for you on this, which I can not do right now.

firstly thanks for your help..
yeah i know this code and technique is very old.. basically my teacher want me to create a chip-8 emulator and i want to do it on visual basic.. do you help me to improve this code in visual basic step by step???

and thanks for providing links... i know very much about chip - 8 now the main thing is to implement it... lets start from keydef???? wht is the best way to assign keydef?? and wht it is keydef(1) = 100 why it is not like keydef(1) = 4? (just for argument)

No problem, I will help where I can if time allows it. I am fairly tied up at the moment, will see if I can start tomorrow some time.

i am w8ing for ur help and now its almost two days... pls help i have to make this project before monday:-(

1. sir please consider this changes also..
declare ram(9016) to ram(4096) because chip 8 requires only 4Kb of memory to run all op codes..

2. stack(256) to stack(16) levels

3. V(256) to V(16) i need only 16 registers of 8 bits each

no need for these functions..
1. DrawScreen_SChip()
2. DrawSChipSprite()
3. ExtendedScreenEnabled()
4. ExtendedSCreenDisabled()
5. ScrollRight()
6. ScrollLeft()
7. ScrollDown

by removing these functions the two functions also changes and that is
1. DrawSprite()
2. Interpret()

Sub Interpret()
    getopcode
    If Check1.Value = 1 Then Text1.Text = Text1.Text + Hex(pc - 2) + ": " + Hex(opcode1) + " " + Hex(opcode2) + " " + Hex(opcode3) + " " + Hex(opcode4) + " -> "
    Select Case opcode1
        Case &H0
            Select Case (opcode3)
                Case &HE
                    Select Case (opcode4)
                        Case &H0:
                            If Check1.Value = 1 Then Text1.Text = Text1.Text + "ClearScreen"
                            ClearScreen
                        Case &HE:
                            If Check1.Value = 1 Then Text1.Text = Text1.Text + "ReturnFromSub"
                            ReturnFromSub
                    End Select
              
            End Select
        Case &H1
            If Check1.Value = 1 Then Text1.Text = Text1.Text + "JumpToAddress"
            JumpToAddress
        Case &H2
            If Check1.Value = 1 Then Text1.Text = Text1.Text + "JumpToSub"
            JumpToSub
        Case &H3
            If Check1.Value = 1 Then Text1.Text = Text1.Text + "SkipIfRegEqual"
            SkipIfRegEqual
        Case &H4:
            If Check1.Value = 1 Then Text1.Text = Text1.Text + "SkipIfRegNotEqual"
            SkipIfRegNotEqual
        Case &H5
            If Check1.Value = 1 Then Text1.Text = Text1.Text + "SkipIfRegEqualReg"
            SkipIfRegEqualReg
        Case &H6
            If Check1.Value = 1 Then Text1.Text = Text1.Text + "LoadRegWithConstant"
            LoadRegWithConstant
        Case &H7
            If Check1.Value = 1 Then Text1.Text = Text1.Text + "AddConstantToReg"
            AddConstantToReg
        Case &H8
            Select Case (opcode4)
                Case &H0
                    If Check1.Value = 1 Then Text1.Text = Text1.Text + "LoadRegWithReg"
                    LoadRegWithReg
                Case &H1
                    If Check1.Value = 1 Then Text1.Text = Text1.Text + "OrRegWIthReg"
                    OrRegWithReg
                Case &H2
                    If Check1.Value = 1 Then Text1.Text = Text1.Text + "AndRegWithReg"
                    AndRegWithReg
                Case &H3
                    If Check1.Value = 1 Then Text1.Text = Text1.Text + "XorRegWithReg"
                    XorRegWithReg
                Case &H4
                    If Check1.Value = 1 Then Text1.Text = Text1.Text + "AddRegToReg"
                    AddRegToReg
                Case &H5
                    If Check1.Value = 1 Then Text1.Text = Text1.Text + "SubRegFromReg"
                    SubRegFromReg
                Case &H6
                    If Check1.Value = 1 Then Text1.Text = Text1.Text + "ShiftRegRight"
                    ShiftRegRight
                Case &H7
                    If Check1.Value = 1 Then Text1.Text = Text1.Text + "RSubRegFromReg"
                    RSubRegFromReg
                Case &HE
                    If Check1.Value = 1 Then Text1.Text = Text1.Text + "ShiftRegLeft"
                    ShiftRegLeft
            End Select
        Case &H9
            If Check1.Value = 1 Then Text1.Text = Text1.Text + "SkipIfRegNotEqualReg"
            SkipIfRegNotEqualReg
        Case &HA
            If Check1.Value = 1 Then Text1.Text = Text1.Text + "LoadIndexWithConstant"
            LoadIndexWithConstant
        Case &HB
            If Check1.Value = 1 Then Text1.Text = Text1.Text + "JumpToAddressPlusReg0"
            JumpToAddressPlusReg0
        Case &HC
            If Check1.Value = 1 Then Text1.Text = Text1.Text + "CreateRandomNumber"
            CreateRandomNumber
        Case &HD
            If Check1.Value = 1 Then Text1.Text = Text1.Text + "DrawSprite"
            DrawSprite
        Case &HE
            Select Case (opcode3)
                Case &H9
                    If Check1.Value = 1 Then Text1.Text = Text1.Text + "SkipIfKeyPressed"
                    SkipIfKeyPressed
                Case &HA
                    If Check1.Value = 1 Then Text1.Text = Text1.Text + "SkipIfKeyNotPressed"
                    SkipIfKeyNotPressed
            End Select
        Case &HF
            Select Case (opcode3)
                Case &H0
                    Select Case (opcode4)
                        Case &H7
                            If Check1.Value = 1 Then Text1.Text = Text1.Text + "GetDelayTimerIntoReg"
                            GetDelayTimerIntoReg
                        Case &HA
                            If Check1.Value = 1 Then Text1.Text = Text1.Text + "WaitForKeyPress"
                            WaitForKeyPress
                    End Select
                Case &H1
                    Select Case (opcode4)
                        Case &H5
                            If Check1.Value = 1 Then Text1.Text = Text1.Text + "SetDelayTimer"
                            SetDelayTimer
                        Case &H8
                            If Check1.Value = 1 Then Text1.Text = Text1.Text + "SetSoundTimer"
                            SetSoundTimer
                        Case &HE
                            If Check1.Value = 1 Then Text1.Text = Text1.Text + "AddRegToIndex"
                            AddRegToIndex
                    End Select
                Case &H2
                    If Check1.Value = 1 Then Text1.Text = Text1.Text + "PointIndexToFont"
                    PointIndexToFont
                Case &H3
                    If Check1.Value = 1 Then Text1.Text = Text1.Text + "StoreBCD"
                    StoreBCD
                Case &H5
                    If Check1.Value = 1 Then Text1.Text = Text1.Text + "StoreRegsAtIndex"
                    StoreRegsAtIndex
                Case &H6
                    If Check1.Value = 1 Then Text1.Text = Text1.Text + "LoadRegsFromIndex"
                    LoadRegsFromIndex
            End Select
    End Select
    If Check1.Value = 1 Then
        Text1.Text = Text1.Text + vbCrLf
        Text1.SelLength = Len(Text1.Text)
    End If
End Sub
Sub DrawSprite()
    v(&HF) = 0
    If ExtendedScreen = False Then
    x = v(opcode2) * 4
    y = v(opcode3) * 4
    For j = 0 To opcode4 - 1
        datax = ram(Index + j)
        i = 0
        If datax >= 128 Then
            DrawScreen
            datax = datax - 128
        End If
        i = i + 1
        If datax >= 64 Then
            DrawScreen
            datax = datax - 64
        End If
        i = i + 1
        If datax >= 32 Then
            DrawScreen
            datax = datax - 32
        End If
        i = i + 1
        If datax >= 16 Then
            DrawScreen
            datax = datax - 16
        End If
        i = i + 1
        If datax >= 8 Then
            DrawScreen
            datax = datax - 8
        End If
        i = i + 1
        If datax >= 4 Then
            DrawScreen
            datax = datax - 4
        End If
        i = i + 1
        If datax >= 2 Then
            DrawScreen
            datax = datax - 2
        End If
        i = i + 1
        If datax >= 1 Then
            DrawScreen
            datax = datax - 1
        End If
    Next j
End If
End Sub

the main reason for all these changes is that i dont wnt to implement super chip 8 instruction i only want to implement chip8 instructions...

the good thing is that i have understand all the code except what is happeing in form_load() and Reset_Click() i also need help in understanding in DrawSprite() function.. and the logic behind that and obviously tips from u to improve it...

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