Action

Declares a subroutine.

 

 

Syntax

DECLARE SUB TEST[( [BYREF/BYVAL/BYLABEL] var as type)]

 

 

Remarks

 

When BYREF or BYVAL is not provided, the parameter will be passed by reference.

Use BYREF to pass a variable by reference with its address. When using the referenced address, you work on the original variable. So a change of the variable inside the sub routine, will change the variable outside the routine as well.

 

Use BYVAL to pass a copy of the variable. Passing a copy of the variable allows to alter the copy in the sub routine while leaving the original variable unaltered. BYVAL will not change the original passed variable but it requires more code since a copy of the parameter must be created.

 

Use BYLABEL to pass the address of a label.  BYLABEL will pass the word address. It will not work for processors with multiple 64 KB pages.

 

Using BYLABEL on the EEPROM is possible but the EEPROM image must  proceed the call with the label name.

 

See also READEEPROM, LOADLABE and Memory usage

 

If you pass a string you may specify the length of the string. This length will be the maximum length the string may grow. This is important when you pass a string BYVAL.

When you for example pass a string like "ABC" to a subroutine or function BYVAL, the compiler will create a copy with a length of 3. This is sufficient to pass it to the sub routine.

But if the sub routine adds data to the string, it will not fit since the string is too short. In such a case you can specify the length. s as string * 10, will create a string with a size of 10.

 

 

See the CALL statement for more details.

 

 

You must declare each function before writing the function or calling the function. And the declaration must match the function.

Bits are global and can not be passed with functions or subs.

 

 

See also

CALL, SUB , FUNCTION , CONFIG SUBMODE

 

 

Example

'-----------------------------------------------------------------------------------------

'name                     : declare.bas

'copyright                : (c) 1995-2005, MCS Electronics

'purpose                  : demonstrate using declare

'micro                    : Mega48

'suited for demo          : yes

'commercial addon needed  : no

' Note that the usage of SUBS works different in BASCOM-8051

'-----------------------------------------------------------------------------------------

 

$regfile = "m48def.dat"                                   ' specify the used micro

$crystal = 4000000                                         ' used crystal frequency

$baud = 19200                                               ' use baud rate

$hwstack = 32                                               ' default use 32 for the hardware stack

$swstack = 10                                               ' default use 10 for the SW stack

$framesize = 40                                             ' default use 40 for the frame space

 

 

' First the SUB programs must be declared

 

'Try a SUB without parameters

Declare Sub Test2

 

'SUB with variable that can not be changed(A) and

'a variable that can be changed(B1), by the sub program

'When BYVAL is specified, the value is passed to the subprogram

'When BYREF is specified or nothing is specified, the address is passed to

'the subprogram

 

Declare Sub Test(byval A As Byte , B1 As Byte)

Declare Sub Testarray(byval A As Byte , B1 As Byte)

'All variable types that can be passed

'Notice that BIT variables can not be passed.

'BIT variables are GLOBAL to the application

Declare Sub Testvar(b As Byte , I As Integer , W As Word , L As Long , S As String)

 

'passing string arrays needs a different syntax because the length of the strings must be passed by the compiler

'the empty () indicated that an array will be passed

Declare Sub Teststr(b As Byte , Dl() As String)

 

Dim Bb As Byte , I As Integer , W As Word , L As Long , S As String * 10       'dim used variables

Dim Ar(10) As Byte

Dim Sar(10) As String * 8                                   'strng array

 

For Bb = 1 To 10

Sar(bb) = Str(bb)                                       'fill the array

Next

Bb = 1

'now call the sub and notice that we always must pass the first address with index 1

Call Teststr(bb , Sar(1))

 

 

Call Test2                                                 'call sub

Test2                                                       'or use without CALL

'Note that when calling a sub without the statement CALL, the enclosing parentheses must be left out

Bb = 1

Call Test(1 , Bb)                                         'call sub with parameters

Print Bb                                                   'print value that is changed

 

'now test all the variable types

Call Testvar(bb , I , W , L , S )

Print Bb ; I ; W ; L ; S

 

'now pass an array

'note that it must be passed by reference

Testarray 2 , Ar(1)

Print "ar(1) = " ; Ar(1)

Print "ar(3) = " ; Ar(3)

 

$notypecheck                                               ' turn off type checking

Testvar Bb , I , I , I , S

'you can turn off type checking when you want to pass a block of memory

$typecheck                                                 'turn it back on

End

 

'End your code with the subprograms

'Note that the same variables and names must be used as the declared ones

 

Sub Test(byval A As Byte , B1 As Byte)                     'start sub

  Print A ; " " ; B1                                     'print passed variables

  B1 = 3                                                 'change value

  'You can change A, but since a copy is passed to the SUB,

  'the change will not reflect to the calling variable

End Sub

 

Sub Test2                                                   'sub without parameters

  Print "No parameters"

End Sub

 

 

 

Sub Testvar(b As Byte , I As Integer , W As Word , L As Long , S As String)

  Local X As Byte

  X = 5                                                   'assign local

  B = X

  I = -1

  W = 40000

  L = 20000

  S = "test"

End Sub

 

Sub Testarray(byval A As Byte , B1 As Byte)               'start sub

  Print A ; " " ; B1                                     'print passed variables

  B1 = 3                                                 'change value of element with index 1

  B1(1) = 3                                               'specify the index which does the same as the line above

  B1(3) = 3                                               'modify other element of array

  'You can change A, but since a copy is passed to the SUB,

  'the change will not reflect to the calling variable

End Sub

 

'notice the empty() to indicate that a string array is passed

Sub Teststr(b As Byte , Dl() As String)

Dl(b) = Dl(b) + "add"

End Sub

 

 

 

Example BYLABEL

$regfile = "m88def.dat"
$hwstack = 40
$swstack = 80
$framesize = 80
 
Dim B As Byte , W As Word
 
Declare Sub Somesub(bylabel Mylabel As Word)
Somesub Alabel
End
 
 
Sub Somesub(bylabel Mylabel As Word)
  W = Mylabel                 ' this points to the BYTE address of the data
  lds _dptrl,{W }             ' point to
  LDS _dptrh,{W+1}
  Read B : Print B
End Sub
 
Alabel:
Data 1 , 2 , 3